Fix some unnecessary reflection.
Actually get reading `bytes` primitive working.
Actually, begin work on next pre-stable minor release.
ByteBuffers in, byte arrays out.

On serialization, handle byte arrays or ByteBuffers for both `bytes`
and `fixed` fields.  On deserialization, always produce byte arrays.
Make read-array and -map loops slightly cleaner.
Switch custom record constructors to positional.
Release version 0.2.0
Begin work on next patch iteration.