Host the documentation somewhere other than rawgit

[nathanwonnacott]

Currently the documentation for this library is hosted at https://rawgit.com/Altran-PT-GDC/Robot-Framework-Test-FX-Library/master/docs/TestFXLibrary.html, but rawgit is at the end of its life (see https://rawgit.com/). Its interesting that it actually even still exists because apparently it has been EOL for a while.

Side note, this is an issue for me now because my company actually blocks rawgit on our network. That probably isn't a problem affecting a lot of people though.