Convert docs from markdown to reStructuredText with Sphinx. Close #260. Fix bug 983834.

Add sphinx-common to VM provisioning for building Sphinx docs. Run `make clean html` inside `docs` to build.
Adding check and sanitizer for double or more // in omniglot's hg path detection
Tolerate bad symlinks when indexing source trees.
Refactor hg path cleaning to use one line
Fix missing lines from highlights on shift-select upwards and then down again
Add logic to only scrollTo a line if it exists in a file
Delete a custom SQLite collation which no one was using.
Merge jumpPosition JS error fix. Close #262. Fix bug 982683.
Merge fix for missing highlighted lines. Fix #263. Fix bug 982660.
Merge branch 'master' of github.com:mozilla/dxr into bug-976558
Making omniglot HG path detection & rewrite add the implied / preceding a path
Add a pref for filter lanaguage.

Adds a config pref for a filter language and a language field to filters. Only filters whose language field contains the config pref appear in the filter menu.
Fix search highlighting on warning searches when the extents
were returned out of order by the database.
Add tests for warning searches.
Make a few tweaks before merging.

* Change "language" to "languages", since it's a list now.
* Don't share a single mutable list between filter instances.
Unabbreviate filter_lang.
Merge the filter_language option. Close #264.

This lets us limit the options in the Filters menu to those relevant to the codebase in question: not showing C++ filters for a Rust project, for instance. We plan to obsolete this before long with proper support for multiple languages within one codebase. Rethinking the Filters menu UI will be required before that.
Fix bug with filters
Try to fix tests under clang 3.3.
Update to peep pre-1.0.

Shouldn't make any difference for us. I'm just testing the new peep changes before releasing peep 1.0.
Merge fix for search highlighting on warning searches. Close #266.