Revert "Revert "Merge branch 'customMapUnits'" so this branch has only changes necessary for a custom JTS geometryFactory"

This reverts commit aea2d6c0a640becf1a37ba98b7d211beb66bbeae.
Merge branch 'master' of https://github.com/filosganga/geogson
Merge pull request #29 from bkiselka/master

handle JTS geometries that are null or empty correctly and do not check lon and lat of Coordinates supporting also metric CRS