Mock a minimal subset of WebRTC.

- only supports firefox dialect of webrtc as of now
- full test coverage
- travis build w/ npm deployment
Added a default dialect to zombese.dialects.

- default dialect is FirefoxZombeseDialect
- updated tests and source to use zombese.dialects.default instead of directly instantiating FirefoxZombeseDialect
- makes it easier to update default in one place, knowing it will work
Updated documentation
Merge pull request #1 from inetCatapult/feat-webrtc-mock

Mock a the minimal subset of WebRTC for testing.