allow selecting exception behavior via options to register
support passing options to constructor to be used as default options
allow callbacks to modify msg using return value
change order of register/unregister arguments
support registering listeners with a decorator
support registering callback with extra arguments
remove opt interface
cleanup some names
change register/unregister to work with single types
register/unregister raise ValueError instead of return codes
clean up type checking in register/unregister
tweak connect/disconnect
rename disconnect to close
more strict type checking for message type
cleanup imports
update readme