Rust issues

[dhardy]

This tracks work-arounds which are waiting for Rust language or standard libary changes.

• [x] std::io::Read::read_exact() — is unstable
• [x] How to copy data from one fixed-size array to another?
• [x] How to simultaneously XOR all entries?
• [x] Use SIMD library?
• [ ] Use NonZero optimisation?
• [ ] Associated constants (see #0025) and BYTES in sum.rs.
• [ ] Error handling: when new try blocks or similar are available some code could be improved.
• [ ] Constant expressions: want max in sum.rs
• [ ] Borrow of item in if-let prevents usage in else part
• [ ] Trait up-casts issue 5665
• [ ] box value notation (Rust issue)
• [ ] Code tag #0018

[dhardy]

SIMD stuff moved to #31

[dhardy]

• [ ] step_by in error.rs: impl<'a> fmt::Display for ReadErrorFormatter<'a>