GitHub release process

[Xcodo]

I finally have a release process that works! There's an example release created by the same YAML file (in a different branch) at Xcodo/rust_hdl/releases/tag/v0.0.0.

I'm not totally happy, but it turns out writing a CI process by snatching half an hour here and there is very inefficient so probably best for other people to make suggestions! @kraigher @Bochlin? Also happy to explain what's going on and add comments if we need it.

Things I don't like

• The workflow runs twice when you push - once for the commit to the branch and once for the tag.
• The tag workflow builds against MSRV when it doesn't need to. Could add more conditionals to the build steps or have a separate release workflow.
• There's a lot of uploading and downloading going on. Could be fixed with a separate release workflow that starts the release then uploads the artifacts as it goes.
• The version filter doesn't actually check for semver, just tags starting with "v".

Things I do like

• It works!
• There is only one workflow so the build is identical to other commits and there's no danger of forgetting to make changes in two workflows.
• There is version checking against the actual binaries.

Closes #45.

[kraigher]

Thank you, this is a big step towards creating a direct value stream from code to the end user.

[Xcodo]

Looks like the first release worked which is great.

@Bochlin the latest release should now be available at https://github.com/kraigher/rust_hdl/releases/latest which forwards to the release page with the version in the URL.