Fri Aug 12 2011
 - match against class Pattern < Hash which has an :optional_keys attr (or :required_keys?)
 - array patterns with min/max ?  (keys 0..n required?)


Also, the words `diff` and `match` seem to get thrown around and
interchanged a lot.
I think I should make it clear that `diff_matcher` was built as a differ
that outputs a textual diff based on what it matched.
ie. by matching `actual` against an `expected` value/pattern/class/proc.

Wed Dec 14 2011
- underline
- string diff