Add matching criteria to kat tests

[kflynn]

Kat doesn't currently test regex matches or header matches. We need to add this.

This might be best done as a MatchTest which extends MappingTest.

[kflynn]

This is opening a larger can of worms than we expected, but it still has to get done.

Current thought is to have MatchTest in parallel to OptionTest. A MatchTest defines how we'll match requests to Mappings, where an OptionTest defines other behavior once a match occurs.

[kflynn]

Some specific things that need more coverage:

• SNI
• header matching

[kflynn]

We've managed to cover SNI and header matching, though not as gracefully as I'd've liked in some cases. Closing this one; we can open other issues as needed.