Add non-legacy mechanism for defining operators

[zdevito]

Currently everything needs to be TH. We should have a way to define a new operator given a cwrap declaration and a templated function that takes the scalar type and processor as template arguments and can do whatever it wants with them.

For methods, this has to be part of the actual library.

For functions, this can be either as part of TensorLib, or as standalone a user can run to produce their own equivalents to Function.h (including optional/output arguments).