Mud

major refactor for paper. merges in github.com/mathematicalmichael/mud-examples into this repo.

rc3 and rc2 are associated with git history that's no longer here.
rc4 is a force-pushed re-working of PR 55 via PR 65

maintains full compatibility with mud-examples but only if latex is installed.

figure filename "tikonov" -> "tikhonov" fixed.

now conforms to type checks

changes behavior in passing a distribution that is not frozen.

option for weighting the initial density by samples if the `weights` keyword is passed to the `DensityProblem` class.

automatic building of documentation using readthedocs. creating tag so that `stable` points to a good looking document.