Transaction: remove TxIn/TxOut exports
Transaction: restrict TxIn input parameters

TransactionIn is only used by Transaction.prototype.addInput and the
Transaction constructor.
It is therefore safe to restrict these input parameters.
Transaction: use TxIn/TxOut consistently
Transaction: move all constants to top
Transaction: remove hash:index notation
Transaction: remove TxIn/TxOut from API
Transaction: add support for custom output scripts
Transaction: renames getHash to getId

Also removes the inherent calculation of tx.hash after a
deserialization.
If a user wants this, they can do it themselves very easily; the
bitcoinjs policy thus far has been to avoid result caching in the
default case.
Especially since a hash is not guaranteed to be the same if the
Transaction is modified after deserialization.

Also adds a test for getId.
Transaction: TxHash no longer stored as hex
unexpectednooowewantgot
txhashhexfix1
txhashhexfix2
Transaction: remove address storage in txOut
Transaction: restrict Transaction constructor
Transaction: fix test name
Transaction: move test to proper section
Transaction: test hex formatting
Transaction: rename script -> scriptPubKey
Transaction: assert signatures as soon as possible