The ChaCha20 stream cipher (RFC 8439) implemented in pure Rust using traits
from the RustCrypto `cipher` crate, with optional architecture-specific
hardware acceleration (AVX2, SSE2). Additionally provides the ChaCha8, ChaCha12,
XChaCha20, XChaCha12 and XChaCha8 stream ciphers, and also optional
rand_core-compatible RNGs based on those ciphers.