Added URL params (request.url_params)

URL params are now present as a `ci_map` member variable of `request`.
* Supports `&` and `;` delimiters in any combination (`?foo=bar&hello=world;black=white`)
* Supports assignments (`?foo=bar`) and single keys (`?foobar`)
I think picking a well tested url parameter parsing library is better here. I didn't check it yet, but some SO replies suggest http://uriparser.sourceforge.net/ .