Stop replacing links inside macros

The textile-formatter runs before the macros: If a macro uses a url as a parameter (e.g. to {{embed_youtube(http://www.youtube.com/watch?v=bqzQ2qrtBeg)}} then these urls are replaced with an inline link (rendering them unusable: e.g. {{embed_youtube(<a href="..." ) - the commit makes sure, that urls inside macros remain untouched.