Added HalSerializer that adds link helpers
Fixed webhook serializer test

1. Updated for the HAL output
2. Changed the expected to be a Hash.to_json.  Allows for line breaks in the code and makes it easier to read/type.  The conversion is very simple, so we shouldn't lose any test fidelity
3. Reversed expected/actual on the test so the output is readable when there's an error
Merge pull request #63 from drewblas/hal_serializer

Hal serializer