Moving and renaming this crate

[dpc]

@kornelski

I'm planning to make a rblake3sum, and I'm thinking about:

• transferring this repo to a different github organization that is not crev-specific
• renaming it to recursive-digest
• removing the build-in blake2 dependency

and then building a rblake3sum (like existing rblake2sum). Just letting you know. If you have anything against please let me know.

[kornelski]

Fine by me.