Support XOR in math operations

[koryphaee]

I am currently working on a project that uses a ulong as a central type in the business logic. It represents a 64bit image hash that I need to XOR with another hash to find the hamming distance. Currently only addition, substraction, multiplication, division, negation and comparison are supported.
I am already using this cool library for my database primary keys but can't use if for the hash yet.

From what I can tell it won't be a lot of work and I will try to create the PR myself.

I already created a separate issue for support for unsigned integers: #16

[koryphaee]

I have the change ready but #18 would need to be merged first since XOR is also supported for the new unsigned types.