rework symatamath

[jlapeyre]

symatamath() is meant to extend functions like * with methods on only types in Base. In other words, to commit opt in piracy. But, these methods are also used internally. I try to define them as methods of a function by the same name in the Symata namespace. But, Julia semantics does not allow two different functions of the same name.

I think I have to use a different symbol, \circ or something for the functions used internally.