adds handling for fetching more than 10 addresses

[netbonus]

adds the ability to fetch an arbirary number of addresses using fetchAddresses

examples:

const addresses = await fetchAddresses({ n: 12 });
// returns 12 addresses

const addresses = await fetchBtcSegwitAddresses({ n: 12 });
// returns 12 addresses

const addresses = await fetchAddresses({ n: 12, startPathIndex: 100 });
// returns 12 addresses starting at the 100th index