Align error codes

[achingbrain]

@libp2p/mplex throws errors with a few different codes, all of which have the prefix ERR_MPLEX_. To make detecting error conditions consistent between mplex and yamux I propose removing the MPLEX_ part of the prefix and that yamux should throw errors with the same code.

The codes are:

• ERR_MPLEX_STREAM_RESET - there was a remote error on the stream
• ERR_MPLEX_STREAM_ABORT - there was a local error on the stream
• ERR_MPLEX_SINK_ENDED - the stream either had it's .sink method called twice after the first source ended or it was closed for writing before .sink was called

[achingbrain]

We should probably split that last one into two error codes 😆

[achingbrain]

This has been done 🎉