feat: defer/lazy load word lists about bip39

[junderw]

We've been throwing around similar ideas for a while, but it's low priority right now.
Pull Requests welcome, though!

I was thinking of making it more generic and making an npm package for each wordlist.

[junderw]

@dcousens I wonder if a lazy loading Proxy might be good...

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy

1. When initializing BIP39, no wordlist is loaded.
2. When any attribute of bip39.wordlists is accessed a getter Proxy takes the name of the thing being gotten and then attempts to require('@bip39/' + name) and return it.
3. If the parent app has name wordlist installed, require will find it and load it.
4. Maybe add hash values for each wordlist to check against known values.

That way, a person looking to add bip39 with English only to their app will do

npm install --save bip39 @bip39/english

Then in their app:

const bip39 = require('bip39')
// bip39 currently has not loaded any wordlists into memory
bip39.mnemonicToSeed(mn, pass)
// doesn't throw an error and still no wordlist in bip39.wordlists. since it doesn't use wordlists.
bip39.entropyToMnemonic(crypto.randomBytes(16))
// this will perform wordlist = wordlist || bip39.wordlists.english
// which will have the Proxy of wordlists do require('@bip39/english') and return that. storing it within bip39.wordlists
// if the require fails, return undefined.

hmmm... I'll have to test it out.

[dcousens]

I don't think many packages is necessary. The only issue is the bundle burden, not npm.

[junderw]

I made a PR with one idea...