Add FreeBSD support
**Is your feature request related to a problem? Please describe.**
Would it be possible to add support for FreeBSD? Pyxel comes with prebuilt libraries and is missing library for FreeBSD. Therefore I cannot run pyxel games on FreeBSD.

**Describe the solution you'd like**
Include prebuilt library for FreeBSD.

**Describe alternatives you've considered**
I don't believe there is, except for running the game on linux instead.

**Additional context**
N/A
