Release keccak v0.2.0

[newpavlov]

Added

• keccak_backend configuration parameter with aarch64_sha3, simd128,
  simd256, simd512, and soft values (#105, #106, #113)
• Keccak struct with a closure-based API for a more efficient access to
  supported backends (#113)

Changed

• Edition changed to 2024 and MSRV bumped to 1.85 (#89)
• Bump cpufeatures dependency to v0.3 (#99)
• AArch64 ASM backend is re-implemented using intrinsics (note that it's still
  enabled by default on AArch64 targets behind target feature auto-detection) (#112)

Removed

• asm, simd, and no_unroll crate features in favor of keccak_backend
  and keccak_backend_soft configuration parameters (#105, #106, #113)
• f1600 and p1600 functions in favor of the Keccak struct (#113)

Fixed

• Use doc_cfg in place of removed doc_auto_cfg feature (#91)

[newpavlov]

Note that the version in Cargo.toml is already bumped.