Added PHPUnit tests for OAuthService

These tests are basically a direct copy from the Twitter service
in the original library by lusitanian. I just copied them over to
get some basic test coverage of the class.
Added myself (crockett95) to authors in example

I added myself to the authors in the PHPdoc block in the example.
This is very direct port from the twitter example in the library by
lusitanian, but needed some minor edits to work with Projectplace.
Added Meta filed -- Readme, Licence, etc

Added README.md and LICENSE.md files to the package. MIT License. Basic usage
in the README. Also added a description for the package in composer.json