API & Documentation site (2)

A resubmission of Pull Request #11617. I ran into some rebase/merge problems which resulted in old commits displaying on the issue tracking page — apologies for this.

> Hey,
As discussed in the mailing list, this pull request aims to relocate the API & Documentation currently in the GitHub Wiki to be accessible from phantomjs.org, with users encouraged to contribute improvements to each page.
> 
> Details on how to maintain the gh-pages branch can be found in it's CONTRIBUTING.md file.
> 
> Please let me know of anything else I can do to help.
> 
> Thanks,
> 
> Jamie, @fold_left