split vector_io_tests off of vector_tests
add data and properties slots to guppy interface tuples
add custon json encoder to handle numpy types
write CRS to geojson
Merge branch 'master' into geojson

Conflicts:
	karta/vector/geojson.py
add new json test data
add featurecollection test
implement read_geojson_features in vector.read (needs test)
make getcrs method public; remove useless try block; remove properties fields from interface tuples
return one geometry per feature
enforce tuple vertex for comparing points
add test for read_geojson_features