libsecp256k1 v0.8.0 released

We'd like to announce the release of version 0.8.0 of libsecp256k1: https://github.com/bitcoin-core/secp256k1/releases/tag/v0.8.0

The most notable changes are: * Addition of a new Silent Payments (BIP 352) module with support for sending and scanning on full nodes. * Addition of a function for overriding the internal SHA256 compression function, useful for plugging in hardware-optimized SHA256 implementations. * Performance improvements in the 64-bit field element implementation, leading to significant speedups for many library functions on GCC and MSVC builds (e.g., up to ~11% for ECDSA and Schnorr signature verification). * Removal of the previously deprecated symbols secp256k1_schnorrsig_sign (in favor of secp256k1_schnorrsig_sign32) and secp256k1_context_no_precomp (in favor of secp256k1_context_static).

For the full changelog, see: https://github.com/bitcoin-core/secp256k1/blob/master/CHANGELOG.md

The libsecp256k1 maintainers