Reference implementation of BIP-0039: Mnemonic code for generating
deterministic keys.

This BIP describes the implementation of a mnemonic code or mnemonic sentence –
a group of easy to remember words – for the generation of deterministic
wallets.

It consists of two parts: generating the mnenomic, and converting it into a
binary seed. This seed can be later used to generate deterministic wallets
using BIP-0032 or similar methods.

See https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki for full
specification.