Convert 'API Error' to raise APIError()

Catch of unhandled exceptions and return them as new API Error 21 - Unexpected API Failure

_decode method that transforms "!!!".decode('hex')errors to new API Error 22: Decode Error
Merge branch 'raise_api_error' of git://github.com/grant-olson/PyBitmessage into grant-olson-raise_api_error
github demanded a manual merge