enable extraction of -1 in _keep_coeff
debug handles args and kwargs
add TR22 to fu.py
factor_terms can remove negative sign or not
TR0 change; futrig adjustments to align output with trigsimp

In all expressions, now, futrig gives an expression that is shorter
(in terms of str length) than trigsimp.
add docstring to trigsimp about compare, fu and futrig
wip