1bm: single binary manager

This is a CLI application. This documentation is for internal details. The crate is named onebm because Cargo doesn't allow crate names starting with numbers.

All the metadata, downloaded binaries, and 1bm itself, are stored under ~/.local/1bm. We intentionally don't use standard directories because we want to make it convenient to manually inspect and change things.

All downloaded binaries are under ~/.local/1bm/bin. The user is asked to add it to PATH to use them.

Metadata are under ~/.local/1bm. Specifically:

• Installed binary list is at ~/.local/1bm/installed.json. It's used to keep track of information like version, dist file, and name of each binary.
• Dist files are at ~/.local/1bm/{FILE_HASH}.1bmdist. The hash is SHA-256 hex digest of the dist file and referenced in the installed binary list.