Support 12 word BIP39 entropy

[richardanaya]

[gilmarwsr]

I created a PR..
#1179

[NicolaLS]

I think it would make more sense to add a "bip39" feature and then use the bip39 crate. Since most users will use this create with this feature it could be activated by default and there could be a --no-bip39 instead too.

• Get rid of bits.rs
• Fully support BIP-39 (not only 12, but also 15, 18, 21 words)

Let me know if you agree, I can also implement it if you want (or @gilmarwsr since they already opened a PR)

[tony-iqlusion]

I think bip39 wasn't used before due to lack of no_std support but that has been corrected.

If someone wants to attempt it, it's something that could be considered.

[NicolaLS]

@tony-iqlusion I started working on it but noticed that the bip32 logic does not interact with any types/api from the mnemonic module anyways. The Xpriv/Xpub can be constructed from AsRef<[u8]> which works with the bip39 crate Mnemonic::to_seed (doc) which requires alloc feature.

So there is really no point in adding bip39 and re-exporting it, forwarding the features would clutter the Cargo.toml and the end-to-end ergonomics of creating a mnemonic and deriving an extended key from it would be the same, users just need to add bip39 separately. With the features alloc and rand_core.

I think it makes sense to just remove mnemonic.rs / mnemonic/ completely, it is out of scope for this crate anyways and the only reason that it was here was that bip39 did not support no-std which is now fixed. Do you agree ?