WIP - Guide

This is a discussion pull request. It's not done yet.

I want to create a "Guide to PouchDB" on the PouchDB.com web site. My inspiration for this is [Ember's website](http://emberjs.com/), which I think is phenomenal.

In short, I think the "Getting started" guide is too simple, and the API has become too complex. We need something in the middle.

I'm basically done except for the "replication" and "conflicts" sections. Feedback is welcome.

The page organization is also total garbage. I just wanted to start writing something, and didn't have time to bother with figuring out how to trick Jekyll into doing what I wanted it to do. I'm hoping that @nickcolley can clean up after me, as he has so many times before. I will probably not have time to work on this again until next weekend, so feel free to go nuts in the interim.