Header-only library for division via fixed-point multiplication by inverse.

On modern CPUs and GPUs integer division is several times slower than
multiplication. FXdiv implements an algorithm to replace an integer division
with a multiplication and two shifts. This algorithm improves performance when
an application performs repeated divisions by the same divisor.

Features:
* Integer division for uint32_t, uint64_t, and size_t
* Header-only library, no installation or build required
* Compatible with C99, C++, OpenCL, and CUDA
* Uses platform-specific compiler intrinsics for optimal performance
* Covered with unit tests and microbenchmarks