Modified existing GitHub class to use new API

Check out the details on the new search API at
http://developer.github.com/v3/search. This also allowed me to
remove the lxml dependency and avoids the problem I saw initially
where GitHub's HTML layout changed and broke the XPath logic.

README.rst and setup.py have been updated with a new minor version
as well as CHANGE entries.
Merge pull request #7 from jhannah01/new-gh-api

Modified existing GitHub class to use new API