0.7.0

release version 0.7

Changes:

- major refactor of geometry hierarchy
    - adds Multiline and Multipolygon classes
    - polygon vertices are double-nested in order to represent sub-polygons
    - only multipart geometries now contain a data attribute
- GeoJSON now attempts to project all data to geographical WGS84 coordinates as
  per https://datatracker.ietf.org/doc/draft-ietf-geojson/
    - `force_wgs84=False` can be set to avoid this behaviour
- multivertex geometries now use CoordString as a data backend, which should
  permit faster operations on the C side
- rename `Line.subsection` -> `Line.to_npoints`
- new R-tree implementation in C
- `projected` keyword argument added to `Point.distance`, `Point.azimuth`, and
  `Point.walk` to control whether geodetic or planar algorithms are used with
  the CRS is not geographical
- replaced polygon membership testing algorithm with a winding number-based test
- implemented fallback algorithm for polygon membership testing in polar regions