libsecp256k1 v0.6.0: MuSig2 Support

libsecp256k1 is a high-performance and high-assurance C library for digital signatures and other cryptographic primitives on the secp256k1 elliptic curve. It is intended to be the highest quality publicly available library for cryptography on the secp256k1 curve.

We are 100% community-funded. Support our work.

"libsecp256k1 v0.6.0 is out! Featuring the highly anticipated musig module and other improvements," announced ncklr.
This release adds a musig module, adds a significantly more robust method to clear secrets from the stack, and removes the unused secp256k1_scratch_space functions.

"In particular, the API functions now use a significantly more robust method to clear secrets from the stack before returning. Thanks to our contributors: @achow101, Cheapshot003 @hhebasto, @pwuille, @real_or_random, Russell O'Connor, @theStack, and all reviewers," added the developer.

What's new

New module musig implements the MuSig2 multisignature scheme according to the BIP 327 specification. See:
- Header file include/secp256k1_musig.h which defines the new API.
- Document doc/musig.md for further notes on API usage.
- Usage example examples/musig.c.
New CMake variable SECP256K1_APPEND_LDFLAGS for appending linker flags to the build command.
API functions now use a significantly more robust method to clear secrets from the stack before returning. However, secret clearing remains a best-effort security measure and cannot guarantee complete removal.
Any type secp256k1_foo can now be forward-declared using typedef struct secp256k1_foo secp256k1_foo; (or also struct secp256k1_foo; in C++).
Organized CMake build artifacts into dedicated directories (bin/ for executables, lib/ for libraries) to improve build output structure and Windows shared library compatibility.
Removed the secp256k1_scratch_space struct and its associated functions secp256k1_scratch_space_create and secp256k1_scratch_space_destroy because the scratch space was unused in the API.