Separate crate for comms wrappers

Standard input and output-like types introduced in 79ad8ef1a7d28fe35f4e7779e5717f09caf3c8f2 can be refactored to a separate, reusable crate. As an additional benefit it will push unsafe and potentially UB-causing bits to another unit, "clearing" the `fleetspeak` crate. See discussion in #6 for more details.