Pyrtools

One minor addition:

- Adds `blue_noise` function to `pyrtools.synthetic_images`

Several small changes:

- adds project_polar_to_cartesian function

- colormap_range now handles NaNs

- updates docstring for colormap range and the various display functions to explain auto0/indep0

- simplifies how we handle filter shapes

- we explicitly check whether a filter is greater than the signal and raise an exception if so (things can get weird in that case)

Initial release.

All the code works at this point, but the documentation could be improved.