Code updates and new functionality

[ ] fix supersmoother which does not work for certain wells
[ ] make pylenm use more general wording such that it can apply to surface water data, not just groundwater; ex. for functions like interpolate_by_well, create a duplicate function interpolate_by_station with the same functionality, and then once all relevant functions are duplicated & the duplicates all work together then we can remove the originals
[ ] implement Kalman filter functionality, from Schmidt et al. https://pubs.acs.org/doi/abs/10.1021/acs.est.8b00017
[ ] Replace or remove richdem package dependency, as it appears to not be used much in the code other than under install_requires in setup.py, and it causes installation issues for some users on Windows e.g. https://github.com/r-barnes/richdem/issues/66

ALTEMIS-DOE / pylenm