1.2.1

Enhancements

• Adds usage and summaries when using swiftenv --help with a subcommand.

• Adds a manpage for swiftenv and swiftenv-install.

  $ man swiftenv
  $ man swiftenv-install

Bug Fixes

• Fixes detecting Swift release toolchains on macOS.
• Fixes an issue where swiftenv install wouldn't emit an error if it couldn't find instructions to install the given version.