Support for query string parameters

I was working on a single page app (coming from a world of server-client app work), and wanted to use query string params as a way to quickly trigger a debug flag to expose some debugging information, or to override mocked AJAX requests.

I created this PR because I saw an issue related to this, and thought you might be swayed by updated tests + this gist that outlines the effect of the feature: https://gist.github.com/pkarl/4758430

Let me know what you think, and if I missed anything in the list of prereqs for a PR. Thanks for pathjs!