Adding Storage#get_unspent_txouts_for_address method.

This method returns all transactions related to one address that are not yet spent.
extend spec for #get_unspent_txouts_for_address
optimize Script#parse

this is about 5 times faster parsing large outputs.
now parsing testnet output c333a53f0174166236e341af9cad795d21578fb87ad7a1b6d2cf8aa9c722083c:0,
which consists of 998kb of "\xff", is feasible
add Tx#normalized_hash

  source: https://github.com/sipa/bitcoin/commit/1173eef630783a822d9a709cfbc22ba91880231e

  todo: remove if not accepted in bitcoind