Create a documentation mirror in GitHub

[JJ]

The problem

With the infrastructure problems, it's clear we should have mirrors in several places, that wouldn't be official by any meaning of the word, but would still help others find the documentation in a pinch.

Suggestions

Create a perl6doc.github.io page, hosted by github, that will have all the static pages of the documentation. We can create a specific user for that or simply use one of our own.