Routing: Add GoToFeature system

A permalink feature that can be useful when writing hyperlink about WebEssentials documentation on others project (as on .weignore template file inline documentation for ligershark/side-waffle#145 ) or web sites.

This could allow the WE web site documentation to be refactored without impacting too much external links in the future.

This is a proposition, feel free to challenge the way I implemented it.