Replace pb2 QueryParser with hand coded parser

Fixes 147

All this does is split the query string. This parser is also primed for being an incremental parser.
Add a test for handling invald strings

fixes #147
Make QueryParser and friends private[http4s]
Allow ';' seperators for query pairs

http://www.w3.org/TR/1999/REC-html401-19991224/appendix/notes.html#h-B.2.2
Add test case from #147.
Update changelog for #147.