Random number generation traits
RngCore is the core trait implemented by algorithmic pseudo-random number
generators and external random-number sources.
SeedableRng is an extension trait for construction from fixed seeds and
other random number generators.
Error is provided for error-handling. It is safe to use in
BlockRngCore trait and implementation helpers
Helper functions for implementing
Error type of random number generators
A random number generator that retrieves randomness from the operating system.