This adds url, data and parser options to the source, and makes
EPSG:4326 the default projection. It also adds a prepareFeatures
method, which is used to load/parse data once the target
projection is known.
The first set geometry is considered the default. As an added bonus, we're back to a single argument constructor. Later, we could allow a schema to be set. This would be done before setting values (calling constructor with no args).
