Make CXXGraph MSVC-Compatible

[nrkramer]

Currently, the library relies on some Unix stdlib functionality (namely, rand_r)

To make the library more portable, alternative functions and C++ functionality should be added to make sure MSVC users can compile. This will go a long way to ensuring portability as well.

We can start by replacing rand_r with a PRNG from <random>

[nrkramer]

I'll open a PR for this once #276 is merged

[ZigRazor]

ok #276 is merged

[nrkramer]

Opened #280