added __repr__ method to Multipoint to simplify instance comparison
Basic read support with GeoJSONReader

The GeoJSONReader will take a file-like object and provides methods to coerce
GeoJSON geometry objects into guppy types. Right now, polygon holes, Features,
and FeatureCollections are not yet implemented.

A set of reader tests have also been added to vector_tests.py.
rename xy to xyfile and add roadmap items