Implement #10 (TBD: docs, better tests, etc.)
Fix syntax for Python 2.6
Remove a debuggish chunk of code
Drop insane sanity check

...which would break relaxed rules in dict keys (see regression test)
Add test for custom validators in dict keys
Add test for a nonsensical case that worked before
Merge branch 'master' into 10-rules-in-dict-keys
Backwards-incompatible changes

* Renamed exception monk.errors.UnknownKey to InvalidKey
* Removed argument dict_allow_unknown_keys from Rule constructor
Add documentation
Document natural/verbose mapping + peculiarities
Merge pull request #11 from neithere/10-rules-in-dict-keys

Rules for dictionary keys