Document optional, wildcards and Regex parameters

Just a quick and small documentation PR.

I had to browse the source to see if I could use optional parameters in the routes' paths. Found everything I needed in your awesome comments.

Even though that code is very nice and easy to browse, I thought other people like me might enjoy getting these directly in the Readme.

PS: Sorry about the trailing whitespaces, I've got Sublime removing them automatically, let me know if it's problem, I'll restore them.