(#2469) - blog post about PouchDB + LevelUP

Looking for feedback on this from @calvinmetcalf and maybe @rvagg / @juliangruber if you aren't busy. I don't want to misrepresent LevelDB or LevelUP, and I'm definitely not an expert on either, but I think the Pouch+LevelUP integration is exciting enough to warrant a blog post.
nit I wrote sqldown from scratch (well if it's based on anything it's based on level.js).