Startinpy

Changed
- the API is now using numpy for the arrays, you can use numpy arrays and the function that were returning lists are not returning numpy arrays
Added
- a proper docs in `/docs`

Added
- startin v0.5 new features:
- interplation with natural neighbour (nni, or Sibson's method) is added.
- saving of the triangulation to GeoJSON is added
Changed
- new name "startinpy" to avoid clashes with the rust lib "startin" on which this project is based on. Since I use a Rust builder (maturin), there were clashes and probably a better idea to call it "startinpy" anyway.