Add type promotion tests for non-elementwise functions #24

Currently the type promotion tests only test elementwise functions and array operators. But there are several other functions in the spec that also participate in type promotion. We should add them to the tests. This should be a question of just going through the parameterizations and adding any function not in the elementwise section that should participate in type promotion. We will need to make some minor generalizations to the tests as some functions only type promote on certain arguments (for example where has three arguments but only type promotes on the second and third). It may be a good idea to look at #21 before or concurrently with this.