Is it desirable to have heterogeneous complex/real operators?

[stephentyrone]

I never had heterogeneous real-complex addition or subtraction, and I've removed the multiply and division operators because of type-inference issues discussed in the README. This is a minor inconvenience for some use cases, and we should investigate ways in which we could make them available--especially multiplication and division, which

• are used more frequently because of the natural interpretation of C as vector space over R
• would allow us to elide a lot of spurious arithmetic operations an get some perf wins