Support releasing multiple packages in a workspace at once

[jwodder]

• When releasing multiple packages at once, should a single commit with all necessary changes be made, or should there be one commit per package?
• When releasing a breaking version of a package, update the version requirements of all other packages in the workspace that depend on it
  • Look into how cargo-release identifies such dependents
• When publishing multiple packages that depend on each other, dependencies will need to be published before dependents