Merge old 'pin-init' repository into 'main'

Historically for pin-init solution in the kernel, there were two attempts,
`pin-init` by me and `pinned-init` by Benno. `pin-init` was created first
and thus it takes the better name. The current implementation is on the
other hand, a combined effort that evolves from Benno's initial
implementation, and was eventually used in the kernel.

It was decided that the combined effort should use the better `pin-init`
name. To preserve the git history and ensures that there is a continuity
between `pin-init` versions, this commit merges two repositories; only the
history is preserved, and no code is taken.

As "conflict resolution", upgrade crate versions to 0.3.0 so it supersedes
the last 0.2.0 release of `pin-init`.

Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Gary Guo <gary@garyguo.net>

Author: nbdd0121