Introduce the `radicle-core` crate for housing data types that are at
the core of the Radicle protocol. The initial data type being added is
`RepoId`. To make the crate as lightweight as possible many of
dependencies are optional and gated by feature flags.
The crate is marked as `no_std` even though it unconditionally depends
on `radicle-crypto`, which is *not* `no_std`. This is to invite
refactoring of `radicle-crypto` to `no_std` at a later time.
This is just enough to get heartwood going.
Some code from the `radicle-git-ext` crate in the `radicle-git`
workspace in repository (rad:z6cFWeWpnZNHh9rUW8phgA3b5yGt) is
copied.
Fintan Halpenny
Lorenz Leutgeb
Lorenz Leutgeb