Merge pull request #13 from akitchen/master

A few minor documentation edits
Incoming properties returns nil.

Closes #7.
Added HYDBlockMapper.

Closes #8.
Added typed mapper that support destinationKeys directly. Closes #12
Fixed headers not being included by default
Fixed README
Typo in spec comment (first line)
Formatting and some minor refactors
Refactored KeyValue mappers
Renamed HYDOptionalMapper -> HYDNonFatalMapper.

Added constructors for HYDMapOptionally which composes
HYDNonFatalMapper and HYDNotNullMapper.

Closes #11.