* added protobuf definition
* added code generated protobuf module
* modified formatter to add \n instead of the sender
* added heka.message and heka.message_pb2
* refactored heka.senders into heka.streams and heka.encoders
* updated tests to use refactored layout
* added tests and code to make sure that HMAC signing for SHA1 and MD5 both work
* added protocol buffer dependency in setup.py
* travis dependencies
* updated UUID JSON encoding to force base64 encoding and decoding
* pulled out heka.encoders:dict_to_msg to heka.tests.helpers
* force uuid to write out bytes instead of strings
* added comment to Message.UUID field