parse protocol bytes via num-traits

[hdhoang]

Also express the message-ACK relationship better.

todo: propagate further up the stack with better error handling.

implement #92, and may help with #20, #63.

[Pzixel]

Self::from_u8(b).expect("unhandled MsgType")

From the docs:

Simple and safe type conversions in to Self. It is the reciprocal of Into.

Note: this trait must not fail. If the conversion can fail, use TryFrom or a dedicated method which returns an Option or a Result<T, E>.

So From shouldn't fail, and by fail they mean any failure, including panic, I consulted the devs some time ago, so you break the core assumptions by that.

[hdhoang]

great, thanks for the pointer! I will move the error-handling somewhere more appropriate.