add support for route meta-data

Declaring meta-data to Compojure routes. I'm developing a Ring-swagger & Compojure-swagger using route meta-data (and code-peeling macros to read those and create route-maps), need a place to declare those without them effecting the runtime behavior of the routes.

https://gist.github.com/ikitommi/8234979

, option 3 works already, but is kinda bad syntax, this patch would allow both options 1 & 2.

One could write a custom versions of the ```compojure.core```-macros with the extra meta-data syntax (like narkisr's Swag does - https://github.com/narkisr/swag), but I thought this could be common stuff for all Compojure.

regards,

Tommi