ENH/BUG: Add predictor diagnostics; fixed intial_guess

Added a class decorator that adds instrumentation and diagnostics output
to any predictor class.

Corrected initial guess behavior in ChannelPredict, and the
corresponding (wrongly) passing test.
Made numba subnet linker use global max size; fixed typos
Prediction velocity fields spanning multiple frames.
CLN: Backslash line continuations in predict.py

Rely on parentheses instead.
Merge pull request #109 from nkeim/predict_diagnostics

ENH/BUG: Prediction diagnostics and bugfixes