- Add `column_row` argument to `rescale_positions`, to use the right axes when
looking up terrain values.
- Convert `rescale_positions` to python/numpy instead of cython, for ease of
maintainability. This does make `rescale_positions` a tiny bit slower, but
it's not a perceptible difference. Rescaling 7,000 vertices was 40 μs with the
cython code and 190 μs with the python/numpy code.