Add BroadcastMessage API documentation

doc/api/broadcast_messages.md

+# Broadcast Messages
+
+> **Note:** This feature was introduced in GitLab 8.12.
+
+The broadcast message API is only accessible to administrators. All requests by
+guests will respond with `401 Unauthorized`, and all requests by normal users
+will respond with `403 Forbidden`.
+
+## Get all broadcast messages
+
+```
+GET /broadcast_messages
+```
+
+```bash
+curl --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v3/broadcast_messages
+```
+
+Example response:
+
+```json
+[
+    {
+        "message":"Example broadcast message",
+        "starts_at":"2016-08-24T23:21:16.078Z",
+        "ends_at":"2016-08-26T23:21:16.080Z",
+        "color":"#E75E40",
+        "font":"#FFFFFF",
+        "id":1,
+        "active": false
+    }
+]
+```
+
+## Get a specific broadcast message
+
+```
+GET /broadcast_messages/:id
+```
+
+| Attribute   | Type     | Required | Description               |
+| ----------- | -------- | -------- | ------------------------- |
+| `id`        | integer  | yes      | Broadcast message ID      |
+
+```bash
+curl --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v3/broadcast_messages/1
+```
+
+Example response:
+
+```json
+{
+    "message":"Deploy in progress",
+    "starts_at":"2016-08-24T23:21:16.078Z",
+    "ends_at":"2016-08-26T23:21:16.080Z",
+    "color":"#cecece",
+    "font":"#FFFFFF",
+    "id":1,
+    "active":false
+}
+```
+
+## Create a broadcast message
+
+Responds with `400 Bad request` when the `message` parameter is missing or the
+`color` or `font` values are invalid, and `201 Created` when the broadcast
+message was successfully created.
+
+```
+POST /broadcast_messages
+```
+
+| Attribute   | Type     | Required | Description                                          |
+| ----------- | -------- | -------- | ---------------------------------------------------- |
+| `message`   | string   | yes      | Message to display                                   |
+| `starts_at` | datetime | no       | Starting time (defaults to current time)             |
+| `ends_at`   | datetime | no       | Ending time (defaults to one hour from current time) |
+| `color`     | string   | no       | Background color hex code                            |
+| `font`      | string   | no       | Foreground color hex code                            |
+
+```bash
+curl --data "message=Deploy in progress&color=#cecece" --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v3/broadcast_messages
+```
+
+Example response:
+
+```json
+{
+    "message":"Deploy in progress",
+    "starts_at":"2016-08-26T00:41:35.060Z",
+    "ends_at":"2016-08-26T01:41:35.060Z",
+    "color":"#cecece",
+    "font":"#FFFFFF",
+    "id":1,
+    "active": true
+}
+```
+
+## Update a broadcast message
+
+```
+PUT /broadcast_messages/:id
+```
+
+| Attribute   | Type     | Required | Description               |
+| ----------- | -------- | -------- | ------------------------- |
+| `id`        | integer  | yes      | Broadcast message ID      |
+| `message`   | string   | no       | Message to display        |
+| `starts_at` | datetime | no       | Starting time             |
+| `ends_at`   | datetime | no       | Ending time               |
+| `color`     | string   | no       | Background color hex code |
+| `font`      | string   | no       | Foreground color hex code |
+
+```bash
+curl --request PUT --data "message=Update message&color=#000" --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v3/broadcast_messages/1
+```
+
+Example response:
+
+```json
+{
+    "message":"Update message",
+    "starts_at":"2016-08-26T00:41:35.060Z",
+    "ends_at":"2016-08-26T01:41:35.060Z",
+    "color":"#000",
+    "font":"#FFFFFF",
+    "id":1,
+    "active": true
+}
+```
+
+## Delete a broadcast message
+
+```
+DELETE /broadcast_messages/:id
+```
+
+| Attribute   | Type     | Required | Description               |
+| ----------- | -------- | -------- | ------------------------- |
+| `id`        | integer  | yes      | Broadcast message ID      |
+
+```bash
+curl --request DELETE --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v3/broadcast_messages/1
+```
+
+Example response:
+
+```json
+{
+    "message":"Update message",
+    "starts_at":"2016-08-26T00:41:35.060Z",
+    "ends_at":"2016-08-26T01:41:35.060Z",
+    "color":"#000",
+    "font":"#FFFFFF",
+    "id":1,
+    "active": true
+}
+```