RFC: Library/MongoDB

This PR introduces capability to integrate MongoDB. More than a PR this is a RFC to see if this is even viable. Feel free to comment as you please, even if you think this is a massive bloat of epic proportions :)

I haven't churned out the documentation yet, since I've yet to ascertain it's viability. 1 or 2 examples maybe found.

I had developed this for my internal use inspired by Alex's library (and its limitations).

P.S. I have purposefully left out Query Builder since I think QB is something which should be implemented above the base class. Also there's a high probability that a Mongo database will be using complex map-reduce/aggregate queries most of the time and/or porting them directly from their intuitive JavaScript counterparts, which are best done in-place.