Making linkify more robust specifically with links embedded in JSON

Updated the link finding RegEx based on updates from Gruber at
http://daringfireball.net/2010/07/improved_regex_for_matching_urls

Made tweaks to allow for arbitrary URL schemes and some special cases
that we choose to handle.
Merge pull request #5 from artificialrobot/master

Making linkify more robust specifically with links embedded in JSON