This is a big piece in the crate smashing puzzle, it involves creating three crates:

• bitcoin-primitives
• psbt-v0
• bip32

Note that primitives may be further smashed but this is a stepping stone we want first. With these 3 crates we should hopefully be able to invert the dependency relationship between rust-bitcoin and rust-miniscript. Additionally many downstream crates will hopefully be able to depend on primitives (and/or psbt-v0/bip32).