API projects documentation grouped into sections & updated with status codes

The API documentation for projects now is structured into major sections that describe
the different aspects when dealing with projects, e.g. hooks, branches, team members etc.
All described methods now contain a list of possible status codes the method can return. A few
methods have extra sample JSON responses and a description if a method is idempotent.
Idempotent methods can be called multiple times while returning the same status code.

doc/api/projects.md

-## List projects
+## Projects
+
+### List projects
 
 Get a list of projects owned by the authenticated user.
 
@@ -55,7 +57,8 @@ GET /projects
 ]
 ```
 
-## Single project
+
+### Get single project
 
 Get a specific project, identified by project ID, which is owned by the authentication user.
 
@@ -92,9 +95,15 @@ Parameters:
 }
 ```
 
-## Create project
+Return Values:
+
++ `200 Ok` if the project with given ID is found and the JSON response
++ `404 Not Found` if no project with ID found
+
+
+### Create project
 
-Create new project owned by user
+Creates new project owned by user.
 
 ```
 POST /projects
@@ -110,10 +119,15 @@ Parameters:
 + `merge_requests_enabled` (optional) - enabled by default
 + `wiki_enabled` (optional) - enabled by default
 
-Will return created project with status `201 Created` on success, or `404 Not
-found` on fail.
+Return values:
 
-## List project team members
++ `201 Created` on success with the project data (see example at `GET /projects/:id`)
++ `400 Bad Request` if the required attribute name is not given
++ `403 Forbidden` if the user is not allowed to create a project, e.g. reached the project limit already
++ `404 Not Found` if something else fails
+
+
+### List project members
 
 Get a list of project team members.
 
@@ -126,7 +140,15 @@ Parameters:
 + `id` (required) - The ID of a project
 + `query`         - Query string
 
-## Get project team member
+Return Values:
+
++ `200 Ok` on success and a list of found team members
++ `404 Not Found` if project with ID not found
+
+
+## Team members
+
+### Get project team member
 
 Get a project team member.
 
@@ -141,7 +163,6 @@ Parameters:
 
 ```json
 {
-
   "id": 1,
   "username": "john_smith",
   "email": "john@example.com",
@@ -152,9 +173,17 @@ Parameters:
 }
 ```
 
-## Add project team member
+Return Values:
+
++ `200 Ok` on success and the team member, see example
++ `404 Not Found` if either the project or the team member could not be found
+
+
+### Add project team member
 
-Add a user to a project team.
+Adds a user to a project team. This is an idempotent method and can be called multiple times
+with the same parameters. Adding team membership to a user that is already a member does not
+affect the membership.
 
 ```
 POST /projects/:id/members
@@ -166,9 +195,15 @@ Parameters:
 + `user_id` (required) - The ID of a user to add
 + `access_level` (required) - Project access level
 
-Will return status `201 Created` on success, or `404 Not found` on fail.
+Return Values:
 
-## Edit project team member
++ `200 Ok` on success and the added user, even if the user is already team member
++ `400 Bad Request` if the required attribute access_level is not given
++ `404 Not Found` if a resource can not be found, e.g. project with ID not available
++ `422 Unprocessable Entity` if an unknown access_level is given
+
+
+### Edit project team member
 
 Update project team member to specified access level.
 
@@ -182,9 +217,15 @@ Parameters:
 + `user_id` (required) - The ID of a team member
 + `access_level` (required) - Project access level
 
-Will return status `200 OK` on success, or `404 Not found` on fail.
+Return Values:
+
++ `200 Ok` on succes and the modified team member
++ `400 Bad Request` if the required attribute access_level is not given
++ `404 Not Found` if a resource can not be found, e.g. project with ID not available
++ `422 Unprocessable Entity` if an unknown access_level is given
 
-## Remove project team member
+
+### Remove project team member
 
 Removes user from project team.
 
@@ -197,14 +238,22 @@ Parameters:
 + `id` (required) - The ID of a project
 + `user_id` (required) - The ID of a team member
 
-Status code `200 OK` will be returned on success. This method is idempotent and call be called multiple
-times with the same parameters. Revoking team membership for a user who is not currently a team member is
-considered success. Please note that the returned JSON currently differs slightly. Thus you should not
+Return Values:
+
++ `200 Ok` on success
++ `404 Not Found` if either project or user can not be found
+
+This method is idempotent and can be called multiple times with the same parameters.
+Revoking team membership for a user who is not currently a team member is considered success.
+Please note that the returned JSON currently differs slightly. Thus you should not
 rely on the returned JSON structure.
 
-## List project hooks
 
-Get list for project hooks
+## Hooks
+
+### List project hooks
+
+Get list of project hooks.
 
 ```
 GET /projects/:id/hooks
@@ -214,26 +263,42 @@ Parameters:
 
 + `id` (required) - The ID of a project
 
-Will return hooks with status `200 OK` on success, or `404 Not found` on fail.
+Return values:
+
++ `200 Ok` on success with a list of hooks
++ `404 Not Found` if project can not be found
+
 
-## Get project hook
+### Get project hook
 
-Get hook for project
+Get a specific hook for project.
 
 ```
 GET /projects/:id/hooks/:hook_id
 ```
 
-Parameters:§
+Parameters:
 
 + `id` (required) - The ID of a project
 + `hook_id` (required) - The ID of a project hook
 
-Will return hook with status `200 OK` on success, or `404 Not found` on fail.
+```json
+{
+  "id": 1,
+  "url": "http://example.com/hook",
+  "created_at": "2012-10-12T17:04:47Z"
+}
+```
+
+Return values:
+
++ `200 Ok` on sucess and the hook with the given ID
++ `404 Not Found` if the hook can not be found
 
-## Add project hook
 
-Add hook to project
+### Add project hook
+
+Adds a hook to project.
 
 ```
 POST /projects/:id/hooks
@@ -244,11 +309,17 @@ Parameters:
 + `id` (required) - The ID of a project
 + `url` (required) - The hook URL
 
-Will return status `201 Created` on success, or `404 Not found` on fail.
+Return values:
+
++ `201 Created` on success and the newly created hook
++ `400 Bad Request` if url is not given
++ `404 Not Found` if project with ID not found
++ `422 Unprocessable Entity` if the url is invalid (must begin with `http` or `https`)
 
-## Edit project hook
 
-Edit hook for project
+### Edit project hook
+
+Edits a hook for project.
 
 ```
 PUT /projects/:id/hooks/:hook_id
@@ -260,12 +331,18 @@ Parameters:
 + `hook_id` (required) - The ID of a project hook
 + `url` (required) - The hook URL
 
-Will return status `201 Created` on success, or `404 Not found` on fail.
+Return values:
+
++ `200 Ok` on success and the modified hook (see JSON response above)
++ `400 Bad Request` if the url attribute is not given
++ `404 Not Found` if project or hook can not be found
++ `422 Unprocessable Entity` if the url is invalid (must begin with `http` or `https`)
 
 
-## Delete project hook
+### Delete project hook
 
-Delete hook from project
+Removes a hook from project. This is an idempotent method and can be called multiple times.
+Either the hook is available or not.
 
 ```
 DELETE /projects/:id/hooks
@@ -276,4 +353,10 @@ Parameters:
 + `id` (required) - The ID of a project
 + `hook_id` (required) - The ID of hook to delete
 
-Will return status `200 OK` on success, or `404 Not found` on fail.
+Return values:
+
++ `200 Ok` on succes
++ `404 Not Found` if the project can not be found
+
+Note the JSON response differs if the hook is available or not. If the project hook
+is available before it is returned in the JSON response or an empty response is returned.