Segwit transaction format

[dakk]

The upcoming activation of segwit, push the need of segwit transaction format support

https://bitcoincore.org/en/segwit_wallet_dev/#transaction-serialization
https://bitcoin.stackexchange.com/questions/49097/what-does-a-segregated-witness-transaction-look-like

The Tx could be a structure like now, but with optional witness fields:

type Witness.t = {
	marker		: uint32;
	flag			: uint32;
	witness		: field list;
	size		: int;
}

type t = {
	hash			: Hash.t;
	version		: int32;
	txin 			: In.t list;
	txout 		: Out.t list;
	locktime		: uint32;

	witness		: Witness.t option;
	size			: int;
} [@@deriving sexp]

The witnessScript reside in a different parte of the tx, but every witnessScript is associated to one txin; could be a smart trick to inflate the wintnessScript inside the txin.

Use this: http://n.bitcoin.ninja/checktx for examples and tests

Tasks:

• Witness abstract data-structure
• Parsing
• Serialization
• Tx hash and tx size for segwit
• Tx vsize
• Witness tests
• Witness tests - P2WPKH
• Witness tests - P2WSH
• Witness tests - P2SH(WPKH)
• Witness tests - P2SH(WSH)
• Witness tests - Hash and sizes
• Block hash and block size for segwit