This adds a new package under dcrutil named txsort which implements a
standard lexicographical sort order of transaction inputs and outputs.
This is useful to standardize transactions for faster multi-party
agreement as well as preventing information leaks in a single-party use
case. It is a modified form of BIP69 which has been updated to account
for differences with Decred-specific transactions.
The sort order for transaction inputs is defined as follows:
- Previous transaction tree in ascending order
- Previous transaction hash (treated as a big-endian uint256)
lexicographically in ascending order
- Previous output index in ascending order
The sort order for transaction outputs is defined as follows:
- Amount in ascending order
- Public key script version in ascending order
- Raw public key script bytes lexicographically in ascending order
