Improve release process

This issue contains various ideas for improving our release process. There's no concrete timeline to do any of these; it's just a dumping ground of ideas right now.

- [This thread](https://www.reddit.com/r/rust/comments/16y8sfw/ring_0170_has_been_released/k387jvl/) contains a lot of interesting thoughts. I would have had largely the same reaction that Brian did, so all of these responses are useful information.
- For users like Fuchsia, who vendor releases and thus don't care about semver, it would be useful if we could automatically publish every commit to a pre-release version, possibly including build metadata such as the commit ID (see bullets 9 and 10 in the [semver spec](https://semver.org/)). We could either do this as a pre-release on the current or next minor version, or we could just use 0.0.0 to indicate that this is orthogonal to our normal version numbering scheme. Currently, we occasionally manually publish alpha releases specifically for the purpose of vendoring into Fuchsia, and this would allow us to automate that process.