lots of clean up of unnecessary attributes bound to the SentryMsg struct
* more clean up of sentry.go
* removed more unnecessary attributes from SentryMsg
* deleted large portions of unused authentication/signature code
dropped hmac_sha1 function as it's not actually called by anyone
throw an error if the dsn is not in the fields of the pipeline pack
added a test back to verify that the final set of bytes sent to sentry are correct
* added test and code to perform checks to ensure the sentry output doesn't panic on invalid or missing field data
Merge pull request #5 from crankycoder/feature/sentry_cleanup

Feature/sentry cleanup