add simplify identities

[latot]

Hi, well this time i propose implement in simplify the expand_func, its very useful specially if we use special functions like beta or gamma, in this case the user can choose how treat the function, in sympy we have 3 options to simplify, "simplify", "combsimp", and "expand_func", actually simplify can cover the combsimp functions, so we only add two.

maybe use directly:

y = python_cmd('return simplify(expand_func(*_ins)),', x);

instead of choose the method, what do you think?

the tests will fail until merge this: #526

Cya.

[latot]

i choose 'special' because are special functions, like beta, gamma, etc.