Automate release process, and other improvements

[PaulSD]

(From #155)

Can we add a js file to "assets"? Cannot find it.

The original "Build" workflow basically just tests the build. There is no easy way to get the built JS file from it.
The original "Release" workflow creates a Release and automatically uploads the JS file to it as an asset. However, it looks like there were several required manual steps (around that workflow) to properly do a Release.

I've reworked things (in this PR) so that the "Build" workflow should upload an asset that you can use for manual testing.
To create a Release, you should simply be able to:

• Merge a PR
• Go to "Releases" in GitHub for this repo
• Click "Draft a new release"
• Click "Choose a tag" and enter the new version number for this release
• If necessary, click "Target: master" and change the branch being released
• Optionally enter a "Release title" and "Description"
• Do not upload any artifacts (If you do then they will be overwritten shortly after clicking "Publish Release". If you need to override the automatic artifacts then you can do so by editing the Release after the automatic artifacts have been added.)
• Optionally check "Set as a pre-release" (The workflow should automatically set this after publishing based on whether or not the version number contains "beta" or "rc")
• Click "Publish release"
• After that, it should automatically build the code and publish the assets to the new Release