Gentoo overlay support

Problem

I cannot compile fluxer with portage as native for Gentoo

Proposed solution

Make a gentoo ebuild for Gentoo, see https://overlays.gentoo.org/ https://wiki.gentoo.org/wiki/Ebuild

Notes (optional)

This would mean I could just update fluxer with my system packages like I would for anything else, it would also pull in build time dependancies as needed, and the -G option of portage could also pull binaires in. Gentoo has a lot of flexibility. I like CPU native optimizations in /etc/make.conf and prefer clang for compiles. Note, some OS like FreeBSD have gcc depricated and are not linux, but do have some translation layers.