Normalize headers

Recreating Pull request on develop branch...

---------

After testing with Frisby.js I was noticing that my resource server grant was failing because node passes in the authorization header all lowercase and this library is looking for Authorization.

I did a little [spec](http://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2) reading and header names are case insensitive. I took some code from Slim to make sure that request headers are in a Ucfirst-With-Dashes format.