Add macOS/Linux binary downloads.

[marcelosousa]

trafficstars

Is there a plan to do a release of binaries? That would be quite helpful for people who just want to try out the tool.

[patrickt]

I agree we should do this. Just a matter of figuring out the correct place to put it. Probably a semantic-0.5.0.0-alpha release or something.

[tclem]

Not quite the same thing, but we are now publishing docker images.

docker run docker.pkg.github.com/github/semantic/semantic