reimplement GeoJSONReader

in a way that maps closer to the GeoJSON standard

rather than having `pull_[geom]` methods, the new class has a single unified
`items` method
reimplement GeoJSONReader

in a way that maps closer to the GeoJSON standard

rather than having `pull_[geom]` methods, the new class has a single unified
`items` method
cast null to NaN in vector properties
Merge branch 'geojson-refactor' of github.com:njwilson23/karta into geojson-refactor

Conflicts:
	karta/vector/read.py
remove obsolete code
remove to_shapely methods; hide vector.stats

- to_shapely redundant with new __geo_interface__ attribute
- stats module not production quality
Merge branch 'geojson-refactor'
clean up namespaces

unify scipy handling in raster.grid
use try block in equality test to avoid attribute errors on non-guppy types
fix bug writing polygon shapefiles

final point duplicated
adds tests for this, and for shapefile attribute tables