Add failing test for regex with quotes.
Specify font face for code-point regex.

This will ensure that if no other syntax highlighting rules apply, a question mark will "pop"
in terms of highlighting.
Add tests for highlighting-related issues.
Remove custom syntax-propertize-function.

The original approach created more problems than it
solved. Additionally, the desired syntax highlighting behavior is
handled gracefully via `rx` and the `rx-constituents` approach I gleaned
from puppet-mode.el.
Merge pull request #73 from elixir-lang/failing-highlight-tests

Fix buggy syntax highlighting behavior involving "?"