Merge pull request #8 from tmedwards/master

Updated the test play/start at passage feature to be header agnostic.
External link syntax parsing changes

* Possibly broken prettylinks are now no longer assumed to be external
relative URIs unless they contain a protocol, or the symbols . / \ or #.
This should make link debugging a bit easier. Thanks tmedwards and
greyelf.
* You can now use external links in the simple link syntax, such as
[[http://example.net]].
* Syntax highlighting updated to match the above.
Updated Wikifier.prototype.subWikify() so that it stops searching once it finds the matching formatter.  Previously, it would continue to iterate over the remainder of the match elements even after finding the matching one.