Allowing the @ symbol to be used in a URL [Fixes #72]

- Added tests to verify that @mention is still working. 

Previously, the code would see the @ in the URL and then bomb; create a new @mention link, and continue. The URL could end up in two states, missing the @ params altogether or a new @mention that makes little sense. 

I was unable to find a reason why @ could not be used in the query params, and it is considered a valid parameter to exist in a URL parameter.