fun deriveSpendingKeys(seed: ByteArray, numberOfAccounts: Int = 1): Array<String>
Given a seed and a number of accounts, return the associated spending keys. These keys can be used to derive the viewing keys.
seed - the seed from which to derive spending keys.
numberOfAccounts - the number of accounts to use. Multiple accounts are not fully
supported so the default value of 1 is recommended.
Return
the spending keys that correspond to the seed, formatted as Strings.