Improve consistency and fix relevancy calculation.

Problem:
  - The word relevancy calculation is case sensitive, all other matching
    is case insensitive.

Improve consistency:
  - Highlighting of elements in the vomnibox is case insensitive; this
    does not match the case sensitive relevancy calculation.

Fix:
  - Bookmark titles, in particular, tend to contain capital letters.
    Unless the query term also contains the relevant capital letters,
    then the term was scored at zero, pushing what seem to be good
    matches to the bottom of the list.  In fact, they were only included
    in the list at all because they happen to pass the
    `RankingUtils.matches()` test.

Conflicts:
	background_scripts/completion.coffee
Refactor RankingUtils.matches() to use splat.

Conflicts:
	background_scripts/completion.coffee
Extend unit tests for RankingUtils.
1. Add additional tests for `RankingUtils.matches()`.
2. Add tests for `RankingUtils.wordRelevancy()`.

Conflicts:
	tests/unit_tests/completion_test.coffee
Bug fix.  Not all query terms matched.
Additionally, add relevant test cases.

Conflicts:
	background_scripts/completion.coffee
	tests/unit_tests/completion_test.coffee
Generalise RegexpCache, refactor, add tests.
This is a no-op, currently.  It's just setting up the RegexpCache
interface for subsequent development.

Conflicts:
	background_scripts/completion.coffee
Adjust word relevancy scoring.
Initial revision.
Added commentry.
Bug fix in recencyScore.
Unit tests were failing, now passing.
Improve comments.
Edit comments.
Additional test cases.

Conflicts:
	tests/unit_tests/completion_test.coffee
Fix incorrect/misleading comment.
Improve comments, refactor unit tests.

Conflicts:
	tests/unit_tests/completion_test.coffee
Incorporate length of matched text in scores.
Fix enter cancels on empty vomnibar.