refactor-864370: Update regexp testing in helpers.audit

If we use `against.match(match)` instead of `match.test(against)` so
we can use a RegExp specified as a string in addition to as a literal.
Minor updates to the assert message for clarity.

Signed-off-by: Joe Walker <jwalker@mozilla.com>
rollup-900114: Review fixes

This is from https://bugzilla.mozilla.org/show_bug.cgi?id=900114#c3
In addition to the requested changes:
* Add 'today' as a synonym for 'now' in the date parser
* Adds tests for now/today/yesterday/tomorrow
* Fix a case where the messages for the check on the d2 parameter were
  given as 'd1'
* Remove some logging from the highlighter

Signed-off-by: Joe Walker <jwalker@mozilla.com>