Breaking changes at the crypto level

[Christewart]

As discussed at #119 @jesseposner is working diligently on getting ECDSA adaptor signatures merged into the secp256k1-zkp.

This presents a problem though: What do we do with DLCs that are using our current temp branch. This is a backwards breaking change to DLCs that are currently in flight.

This problem will occur again when we incorporate Schnorr as far as I know.

I'm definitely in favor of these break changes being obvious for users rather it being hard to detect. We can use TLV types but I know @nkohen has expressed concern about burning TLV types for minor things like this, but i'm unsure what else can be done.