Bugfix - reversing byte order for value

Value bytes should be reversed in ```new TransactionOut(data)``` so that it is LE

The correct example is demonstrated here: https://github.com/cryptocoinjs/btc-transaction/blob/master/lib/transaction.js#L132

I have included tests to make sure that the 
1. byte order is correct
2. ```new TransactionOut()``` and ```Transaction.addOutput()``` produce the same byte order