[WIP]: Adding arm builds.

[afinch7]

I want a build of fly.rs that runs on arm hardware like raspberry pi. To make that work I need a version of the v8 lib compiled for armhf/arm64.

[jeromegn]

Nice, does it work? 😄 Looks like this didn't build in travis 🤔

In fly.rs, we've started building inside a Docker container (including v8, using multi-stage builds) to get everything neatly contained. It's based off alpine and builds a statically-linked binary for production. This repository is still useful for all other use cases (other OSes, local development, etc.)