WIP: Add mechanism for location prediction
TST: Added failing and baseline tests for simple prediction.
WIP: Refactor prediction implementation. Add tests and working most-recent-velocity-based predictor.
WIP: Use n-dimensional interpolator.
WIP: Rename prediction engine classes, to avoid confusion with "predictor" functions.
WIP: Beginnings of demonstration notebook for predict.py
WIP: Fix division-by-zero bug in predict velocity field calculation.
Changed cKDTree leaf size to constant.

Optimal leaf_size is function of data's spatial structure, not of N.
15 seems reasonable.
ENH: Added ChannelPredict for channel flows.
API: Switch default linker to "auto" (numba when available)
Faster interpolation for ChannelPredict; simple tests
DOC: Finished example notebook; better docstring for ChannelPredict
BUG: In ChannelPredict, interpolation is now based on bin centers.