Support 12 word BIP39 entropy

[richardanaya]

No description provided.

[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.