Fix building the webapi docs.

My changes to define string types using six.text_type means that the type can
now be 'unicode' instead of 'str'. This works fine in the API, but the docs
generator didn't know how to interpret that.

Testing done: Built the API docs.

Reviewed at https://reviews.reviewboard.org/r/4992/
Tweak markdown escaping to be less eager.

The markdown escaping was still pretty overzealous, escaping -, +, and #
characters even when they didn't affect the markdown output. This made the
source text annoying to read.

I've made the regexes more complex to handle these cases.

Testing done:
* Verified my assumptions about how these characters are treated in the source
  text.
* Ran python and javascript unit tests.

Reviewed at https://reviews.reviewboard.org/r/5005/
Fix unicode errors with bzrlib.

bzrlib is even more janky than I thought with regards to its treatment of
strings--it expects repository locators to be str objects with ascii encoding.
This means, I believe, that if you had a unicode path on your filesystem, you
couldn't have a bazaar repository in that path.

Encode all the things before passing them into bzrlib.

Testing done:
Ran unit tests. Some bzr things are failing for other (configuration/setup)
reasons but there are no more unicode/string errors.

Reviewed at https://reviews.reviewboard.org/r/4993/
Update a bunch of stuff in the docs.

I just did a read-through of the docs to check for things that are out of date.
Aside from having to completely rewrite the 'post-review' page, and many of our
screenshots being old and out of date, there were a few text changes that
needed to be made:

* The reference to "Getting Started" in the codebase "Custom Forks" page wasn't
  correct.
* The "Unit Tests Fixtures" page still listed test_reviewrequests and didn't
  have any information about the new `TestCase` class.
* The minimum browser versions still said we supported IE7.
* The "What is Code Review" page had out of date information about the state of
  our support for post-commit review.
* There was a typo in the paragraph about the "Bugs" field.
* There was no documentation for the "Depends On" field.

Testing done:
Built user manual and codebase html and looked at the results.

Reviewed at https://reviews.reviewboard.org/r/4981/
Add missing files for the manual.

The web API docs were complaining about some missing files, which
.gitignore was hiding from me. This should fix the docs builds.