Fix for embedding code from github
Add option for custom js (like custom css)

* Add a new 'js' flag to indicate you want to embed a file named 'custom.js'
  which should exist at the root of the wiki
Merge pull request #661 from simonista/custom-js

Add option for custom js (like custom css)
Update README.md
Update README.md
Merge pull request #660 from simonista/fix-github-links

Fix for embedding code from github
Merge branch 'master' into feature/gollum-lib

Conflicts:
	lib/gollum/markup.rb
	test/test_gitcode.rb