SynchronizedSet() requires manual synchronisation when iterating
over it. When returning an iterator make a copy of the set first
to avoid issues with users iterating.

If we multiple long lines in succession the start index got
miscalculated and part of the latter lines discarded.

Move message processors into their own package
Update ktor

After allowing multiple names we started ACKing only the preferred
name, even if the server hadn't advertised it.

Closes #13

Closes #11

Move handlers to their own packages
Update JUnit

Closes #9

Fix regression with capability negotiation

This allows more options to be added nicely in the future,
and hides the implementation details from library users.

Only annotate internal methods, suppress the messages otherwise,
so users of the library don't have to deal with warnings

Add dokka and a dependency checker plugin

Don't bother building on JDK9, just 8 + 11 should cover it

Closes #8

Closes #2