Add default dtype to constructors and other complex methods to allow flexibility for users

[rmclimber]

I would like to use this package with higher precision, so I have added the ability to pass dtypes.

I went through all the functions and classes in the package. For each class in complexLayers.py, I added a dtype=torch.complex64 optional argument to the constructor and a self.dtype=dtype class member. In class methods, I replaced torch.complex64 with self.dtype. For each method in complexFunctions.py which uses the dtype at all, I added a dtype=torch.complex64 optional argument and replaced torch.complex64 with dtype in the method body.

Without a testing suite I can't verify nothing broke with confidence, but I used default arguments so that current users do not need to change their function/constructor calls. Pretty sure this should be entirely backward-compatible with existing work.