Remove deprecated things #183
Description
We've retained an ability to call differentiation methods with a params list and options dictionary, and we have kept around old method signatures like meandiff and constant_velocity that are really just particular hyperparameterizations of more general methods. But as of the v0.2 release ("Revamped") these are deprecated and raise warnings. Catching, warning about deprecation, properly using inputs given in the older way or calling the proper generalized functions, and then testing all that actually takes up quite a bit of code and makes our docstrings and readthedocs documentation significantly more complicated than they could be. It would simply everyone's lives to actually go rip it out, except for anyone running old code.
Old code will now raise warnings that coach users on how to update their scripts. Now that this has been set in motion, let's start a clock: If someone has not updated their code by the time of the next major release after at least a year from today, then we give ourselves freedom to break backwards compatibility and accept their failures and potential flock of issues here, directing them to update their code or use earlier versions from PyPI.