MAJOR UPDATE - 4.0 Unforgeable Groups for Bitcoin Cash

This was prompted by some discussions I had with imaginary_username and after realizing that the groupID can be used as a "witness" to construct unforgeable Script covenants. These would then let us implement all advanced supply and metadata management features from within Script, while letting token amounts be free P2PKH citizens, giving us the best of both worlds, consensus and Script.

Also, pure "carried witness" mode is supported, which would enable fixed-size inductive proof covenant contracts that would work the same as PMv3 "detached witness" examples but reconstructing the groupID witness instead of TXID as proof. They could use the groupAmount 8-byte field to store some contract state, which I believe would simplify those contracts a lot, and make the proofs lighter.

4.0 Unforgeable Groups

• Simplified the output format and consensus layer
• Generalized output groups as "carried witness", having only the GENESIS rule enforced
• Amount field is now optional and indicated using the LSB of groupID so the whole group must have or not have it
• Native token groups and Satoshi token groups (aka "holds BCH") are then a more restricted variant of a generalized group, having token logic enforced over respective amount fields, and NFT logic enforced over amountless token groups.
• 0-amount indicates "singulary" i.e. an infinite source or an infinite sink which allows token amount creation and destruction
• Any advanced features, such as metadata updating, are to be implemented using unforgeable Script covenants, as demonstrated in the examples section
• Reworked CHIP sections