add WalletKey required dependency
Buffer.concat expects an array of buffers
util is in bitcore/util/util.js - fixes all uses of util
valueNum needs to be in satoshis, but datastore.outputs[addrStr] is in bitcoins
get rid of redundant util -> replace with coinUtil
add write_datastore after signing for a wally wallet

...requires proper handling of asynchronous rpc call, hence adding async.js as
a required package.
allow scripthash & multisig to be signed more than once
don't append serialized script if it's already there
sometimes scriptSig.chunks has length 0
fix bug where you had to sign with 3rd key first
bring p2sh multisig in line with BIP 0011

1) remove placeholders when a p2sh multisig transaction has been fully signed.
2) prepend the script with OP_0
https://github.com/bitcoin/bips/blob/master/bip-0011.mediawiki
https://github.com/bitcoin/bips/blob/master/bip-0016.mediawiki
move script functions to bitcore
Merge pull request #4 from ryanxcharles/bug/multisig-bugs

write signed transactions for wally wallets, plus several bug fixes