Completing inside a word used to try and take the whole word into
account. This is not typical completion behavior, and often not what
you want. After this change, the addons only take the part of the
word in front of the cursor into account.

- Added link to tests on mode page
- More consistent naming with CSS spec (some of the previous var naming was completely incorrect/misleading)
- Improved highlighting
  - Match vendor prefixes
  - Check for known properties and values (known properties are bold, unknown are not)
  - Added highlighting for media queries
- Cleaner stacking of state

Since v2 is the canonical CodeMirror at this point

So that I can put other doc-related stuff there without polluting the
root dir.

It's tiny anyway, no need to force people to include yet another file.

This normalizes the classes used by most of the modes
(reStructuredText and diff didn't fit in), and makes them all
reference a central style sheet (under theme/). It also adds a theme
option that can be set to change the theme, and defines a few
different themes (some based on old mode colors).