add support for unsigned long long

Need to be able to format the following without any casting

std::cout << fmt::str(fmt::Format("{:x}") << 0xAEull) << std::endl;
std::cout << fmt::str(fmt::Format("{:x}") << 0xAEul) << std::endl;
std::cout << fmt::str(fmt::Format("{:x}") << uint64_t(0xae)) << std::endl;

I believe the last one is already supported. I did not add the tests for this. can't get generated make file from cmake to do anything on linux or work on windows. But was able to compile the VS solution.