Paths config

Wish  you had  a dev branch or something so I didn't have to submit this to master, but time to suck it up and show some confidence in my code I guess ;)

I'll change the path mapping logic to use the "@alias" format once I get back from lunch.

I still think there are good use cases for allowing users to change the baseUrl to something other than `cwd`, so maybe we could think of a different token to use for that reference than `:cwd`.  Maybe `:root` ?