Fix for Issue #11 - adding ^ and * to link character set.

Hi, per the subject I added a few characters to the links regexp. This would fix a few broken links on my site. I added tests with the links that were broken, please let me know if you would like any further information or if there is any issue with this. 

Note, four of the unit tests were failing on my install. Please see: https://gist.github.com/crw/5329229. These are still failing after my changes. :)