Initial REST implementation for marketo API

A better overview of the implemented functions can be seen on the branch's [README](https://github.com/usermindinc/node-marketo/tree/ak-first_commit)

This is an initial stab at implementing a marketo library that integration-marketo will work off of. I was not able to find a node library out there that uses the REST API, but will be happy to switch to one if it pops up.
Looking around a little more, it looks like somebody [complained about this to Marketo](https://twitter.com/MarketoDev/status/526884738410508288) 21 days ago and compared [the typical flow vs Marketo's flow](https://gist.github.com/blairanderson/db4ab904193327dd29e5).