Add the cow_qs module for query string parsing and building

Includes functions to encode and decode percent encoded strings
that follow the application/x-www_form_urlencoded format.

Query string parsing should be 3 times faster than the code
that was in Cowboy, and will also create less intermediate
variables.
Remove some pointless comments
Update cowlib to 0.4.0

Add support for query strings, optimize cookie date building.