add all possible parameters to Voice Post
parse twilio error in voice & move logic to common
so much refactoring

interfaces everywhere
closes #7
move remainder of post logic to common interface
remove unused method & renaming
fix voice post struct
Merge pull request #8 from natebrennand/refactor

Refactor
Adding twiml package

Currently only supports Say, Play, and Record verbs.
Changing Render to return a Reader instead of a string
Adding go get -t in travis install step

This way test dependencies will get installed.

Goddammit travis.
Fixing enclosing Response tag in twiml
Changing Render to RenderReader

The Render method now returns a byte slice instead of a Reader
interface.
Adding end-to-end test to twiml
Renaming Twiml struct to Response
Massive refactoring into separate files and interfaces