Base64 encoding/decoding protocol buffers

After encountering serialization issue with the raw payload and
IronMQ’s expectation that the payload will be json, moving the payload
to an intermediate data format is required.  The decision to use B64
was based on the following stackoverflow post:
http://stackoverflow.com/questions/1443158/binary-data-in-json-string-so
mething-better-than-base64
Test updated to reflect the new use of Base64
Packaging out B64 payload in json

This payload should always be json
Merge pull request #2 from harrystech/base64_payload

Base64 encode protocol buffer payload prior to sending message to IronMQ