Creating a generic file reader interface

This is a WIP still, but the idea is to add drag and drop support for GIS files onto the map.  I created a reader for a reduced geoJSON specification that is attached to the `glOsm` example as a proof of concept.  I haven't fully fleshed out the base `fileReader` class.

I think I will change the interface a bit so that rather than providing a single reader type to the map, there will be a function that will try to open the file with every available reader until one succeeds.  Then, there will be a map option to enable or disable drag and drop.
Simple ones for now.  (MultiPoints, Points, and LineStrings)  I think it is better to have a geojson reader here rather than vgl so that it can add features though the feature api.  I'm just fleshing out some ideas here to make the json reader extendable so it can support a more arbitrary objects.  You can customize how coordinates/styles are stored, etc.