Setup emscripten

This is a GitHub action to setup an emscripten environment. You can optionally specify which sdk you want to install.

In actions.yml:

steps:
  - uses: numworks/setup-emscripten@v1
    with:
      sdk: latest-fastcomp
  - run: emcc --version

How to update this action

Before merging a PR to the master branch, make sure you removed the node_modules directory and ran npm install.
Once CI is passing, update the "latest" tag.