Changed interface and added format options

Hey man, this is actually the first time I've done a pull request and since I'm pretty sure this changes how you fundamentally use the module, so I doubt you'll accept it, but figured it's worth a shot.

I wanted to be able to pass my created express app in to the module in order to add the crud methods, rather than patching the express module, so I changed that interface.

Also, I needed a way to format the JSON data being sent back to the client, so I added an options object which is passed in with the app and can have a formatResponse method which has the response piped through it if it is present.

I added some more documentation to the README for these features and updated the tests to current tests to reflect the change, though I know I should add some more coverage for the formatResponse option.

I think formatting of the response data is a much needed feature and though the change in interface was more a preference thing, I can't think of a way to cleaner way to parametrize the module without giving it a function interface.

I feel this tool is pretty useful as is, but I'd like to help improve it without fragmenting if possible, let me know what you think on these points.

Thanks!

Seems like this may not bee needed.  Thoughts?