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
Helper functions for implementing
Error type of random number generators
A random number generator that retrieves randomness from from the operating system.
The core of a random number generator.
A random number generator that can be explicitly seeded.