Add GeoInterface.convert methods

[rafaqz]

Would be nice if convert worked ;)

We can add a convert(WellKnownGeometry, geom) method now too.

[evetion]

Yeah, first pirating GeoFormattypes? Not sure if that clashes with ArchGDAL.

Will make type wrappers that also store dimensionality.

[rafaqz]

It wouldn't be pirating in the module method. But yes maybe ArchGDAL should do the convert to GeoFormatTypes wrappers.