Binary serialization over pipes

[pvdrz]

This binary serialization over a pipe comes up in other places. perhaps a bit of abstraction could help with the buffer sizes and ser/de steps, e.g. Pipe<T: BinSerDe>, impl BinSerDef for i32 { const NUM_BYTES: usize = 4; /* .. */, Pipe::write(val: &T), Pipe::read() -> io::Result<T>, etc.

Originally posted by @japaric in #468 (comment)