New TOPAS documentation website goes live!

I have moved our documentation from the old PDF document to a website hosted by ReadTheDocs: http://topas.readthedocs.org

They also host a PDF version: https://media.readthedocs.org/pdf/topas/latest/topas.pdf

From the user perspective, I hope that this will help to discover features of TOPAS more easily and find solutions to their problems more quickly. Hyperlinks now connect related sections.

From the developer perspective, this should make collaboration easier for documentation and supports documentation versioning. We can also now link to documentation sections when replying in the User Forum, which will hopefully save some time.