renamed to GitHubAPI, merged models into main assembly, added functions for issues & issue comments

renamed because this isn't just for csharp (although it's written in it)
also wanted to limit the - in the namespace as this is very rarely seen
in .net
added VSTests alongside Nunit tests because the express products can't
use the Nunit test adapter extension (which sucks)
FYI A test project can have an App.config, which i think is a bit nicer
than the .dll.config you had people using