Tool for generating sha256 initializiation with fixed midstate from BIP340 tagged hash

[theStack]

New secp256k1 modules often take use of BIP340 tagged hashes, with corresponding functions to initialize _sha256 objects with a fixed midstate for efficiency reasons. Right now there seems to be no standard way to create these functions, presumably every contributor does this in a slightly different way (I guess all ways involve cluttering the code with printf statements though). I was wondering if it's worth it to provide a small tool for that, which could also be useful for reviewing.

Proof-of-concept (not involving the build system yet): theStack@009cac6

[real-or-random]

Last time I needed this, I used this Python library: https://github.com/cloudtools/sha256. I believe that's a bit simpler than maintaining a C program (with build system integration, etc.)

Of course, we could also add a small Python snippet that prints a BIP340 midstate explicitly.