add an action to deploy to github pages when pushed to master.

[tonyfast]

fixes #75

[rgommers]

Thanks @tonyfast! Looks great, just a few comments. The last one is the most important, latest/ needs to be in the URLs to not break incoming links.

[tonyfast]

i resolved your comments. i set up the actions to create an artifact of the documents so they can be previewed. the github pages deployment only updates on changes to master.

[rgommers]

Tested on my fork and fixed all remaining issues, let's give this a go! Thanks @tonyfast!