Also, add an assertion that the WSGIResponse gets its 'Content-Length'
header correctly set.

See:  https://bugs.launchpad.net/zope2/+bug/789863

This change applies Leo Rochael's patch from:
https://bugs.launchpad.net/zope2/+bug/789863/+attachment/3624368/+files/0001-Make-the-request-object-unpublishable.patch

And the ideas from Richard Mitchell's patch at:
https://bugs.launchpad.net/zope2/+bug/789863/+attachment/3625765/+files/request_object.patch

Manual cherry-pick of:
81e1fc07
b3f2cf76

[ci skip]
(cherry picked from commit 81e1fc07)

- Add docs for installation into a virtualenv.
- Update Sphinx paths to use '_' prefix.

(cherry picked from commit 6b96bc75)

This reverts commit 367a7ea5.

This reverts commit 246610dd.

See #11.

Fixes #12.

Prevent leaked connections when broken 'EndRequestEvent' subscribers raise

Fixes #16 on the master branch.

- Include ztk-sources.cfg and ztk-versions.cfg
- (without accidentally including .installed.cfg or .mr.developer.cfg)
- Exclude built Sphinx docs

- Move changelog to root project directory.  Leave a stub behind for Sphinx.

- Move 'doc' -> 'docs' and fix up.

- Use newer Sphinx locations for support files,  build targets.