Geojson reader from string

@cjh1 Hopefully this works for you.  It depends on my other PR, just for the asynchronous jasmine test.  The read function will take a file/string/object.  See the minimal test [here](https://github.com/OpenGeoscience/geojs/blob/44d564de8f3cd160d7177a10f064c6f20db5d0bb/testing/test-cases/jasmine-tests/geojsonReader.js).