Download and run cargo-tarpaulin from GitHub releases

[garyttierney]

This is mostly a draft right now, but should be fully functioning (though you'll have to invoke cargo tarpaulin yourself, this action is only installing it right now). Some things still to do:

• Generate dist/index.js, only sources are in here now (maybe we add a pre-commit hook for this)
• Check for missing cargo-tarpaulin versions (if someone requests an invalid version, we should be able to identify that)
• Resolve the latest version to the current GitHub release.
• Actually run cargo-tarpaulin as part of the action.
• Pass user supplied options through to tarpaulin.

We're using the version that is published to tarpaulins GitHub releases page instead of pulling it from crates.io. This cuts a considerable amount of runtime off of the job (10m vs 1-5s). This works because the GitHub actions virtual environment is identical (for all intents and purposes, they're both using Ubuntu latest) to the environment that tarpaulin is being built in.

[JP-Ellis]

Any update on this pull request? It would be very helpful to have this 👍 (if I get time, I might be able to help in a couple of weeks if this is still pending).

[djc]

Hey @svartalf, could you re-review? Would be great to have this!

[svartalf]

https://github.com/marketplace/actions/rust-tarpaulin 🎉