MongoDB connector for points, lines and polygons

We need to add a map backgrounnd to our navigation web-app. Mapnik in a combination with a client-side mapping engine solves problem well. But we want to use a MongoDB as a datasource for Mapnik because we use MongoDB as a storage already. I have implemented input plugin to do that, see the demo on my fork README.md.

P.S. I've also changed a coding style in the sources to work more comfortably. If it's important, i can revert it back :-)