Fu

futrig now mimics the old `_trigsimp` routine and pattern matching using the Fu-transforms. The Fu-algorithm is also implemented with additional transforms that were not described in the original paper. @pernici has significant improvements which might be better to accomplish trigsimping, but until then this fill the gap for patterns, robustness and efficiency.  

I learned a lot about working with the expression tree more efficiently from Mario's work. Whatever is good in this PR is largely due to his influence. Many thanks to him for his comments during this work and his own code that kept me working at the code used here.