* update master key generations using "Bitcoin seed" as hmac key following BIP32
* use `"mnemonic" + passphrase` as salt for pbkdf2 following BIP39
* test generated addresses and compatibility with BIP44
* check generated public keys
* test children private keys
* update MasterKey to be a constant
* don't export salt and masterKey constants
* use `crypto.FromECDSA` to get the hex representation of the priv key
* use empty pwd for the generation of the BIP39 seed, keeping pwd to encrypt keys
* add comment before the seed generation with empty passphrase
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