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`)
@ipkn I am happy to replace this code with the parsing code from a different library, if that's what you're asking?