Load management send slow down when close to limit

This is a copy of #248 with the two requested fixes added on top (255 as max byte and 65535 as max word).

The commits were actually made before I was aware of the new commit message rules, so the messages are still too long. Sorry about that…
Any reason for not providing constant instances for this class (or maybe even use enum)? E.g. `Accept.ACCEPT_SLOW`, `Accept.ACCEPT` and possibly even `Reject.FORWARD_OVERLOAD` and similar.