Abstraction on HTTP clients and add Requests client support (http://requests.ryanmccue.info/)
Rename Http adapters
Add PhpUnit to composer.json and update Guzzle version
Add some comments and code cleanup
Bump version number on missed user agent string
Merge branch 'release/v0.2' into develop

* release/v0.2:
  Bump version number on missed user agent string
fixed escape character
Don't transform artist lifespan dates into \DateTime

Some artists begin and end date are limited to only a year which breaks the constructor
Merge remote-tracking branch 'upstream/develop' into develop

Conflicts:
	src/MusicBrainz/Release.php