Fix: oops

Merge pull request #4 from dogeorg/segwit-block-parsing

Fix: added SegWit parsing in DecodeBlock/DecodeTx (occurs in AuxPoW)

The new approach exactly mirrors the parsing logic in Core to avoid inconsistent parsing outcomes.
Now also detects invalid script size and varInt size as per Core, which typically happen when parsing goes astray.

Also added DecodeBlockErr/DecodeTxErr that return error details for debugging issues like this.

Merge pull request #3 from ronny/bip32key-child-number

Add `ChildNumber()` to `Bip32Key` @ronny

P2PKHScript, P2PKHScriptFromAddress, P2SHScript, P2SHScriptFromRedeem…

…Script

Removed input script length check, because unsigned script inputs
have an empty script.

EncodeTx with tests

Binary Encoder and Decoder from DogeNet, with tests

HexDecodeReversed undoes HexEncodeReversed, with test (oops)

HexDecodeReversed undoes HexEncodeReversed, with test

fix: incorrect zero padding on Koinu fractional part

Block and Tx parsing: optionally calculate hashes; copy-reversed