First cut at replacing core protocol method check with walker:
 - All old tests for check pass with new implementation
 - More perf tests pending, but initial investigations suggested 5x+ faster validation
 - Renamed String and Number to Str and Num to avoid clashes with java.lang classes
 - Applications for increased flexibility of new protocol enabled, but not yet added
Add experimental schema-driven coercion
Support primitive array typehints
Address PR comments
Merge pull request #52 from Prismatic/walk-refactor

Walk refactor