3826: reverse tan double angle
3821: simplify trig to exp and vice versa

recognizing I*tan(x) and tanh(x) will take a little more work
factor exptrigsimp out of simplify
update exptrigsimp docs
edit docstring
exptrigsimp recognizes tan and tanh
use TR2i to do -> tan/tanh
remove numerical testing scaffolding
document use of simplify in exptrigsimp
edit inline spelling
allow E to rewrite as cos/sin
recognize cosh and sinh in exptrigsimp
reposition exptrigsimp and edit docstrings
extend exact values for bessel functions with half integer nu