Rewrite event mixin, add signalHandleable
Rewrite event mixin, add signalHandleable

tecnogram888/prosemirror,adrianheine/prosemirror,yakovenkodenis/prosemirror,jacwright/prosemirror,yakovenkodenis/prosemirror,adrianheine/prosemirror,ProseMirror/prosemirror-markdown,salzhrani/prosemirror,salzhrani/prosemirror,ligthyear/prosemirror,bengler/prosemirror,kiejo/prosemirror,kiejo/prosemirror,salzhrani/prosemirror,tgecho/prosemirror,jeffplourd/prosemirror,jarrodh/prosemirror,jeremiak/prosemirror,tzuhsiulin/prosemirror,mattberkowitz/prosemirror,jeremiak/prosemirror,adrianheine/prosemirror,jeffplourd/prosemirror,tzuhsiulin/prosemirror,ligthyear/prosemirror,mattberkowitz/prosemirror,jacwright/prosemirror,jarrodh/prosemirror,tgecho/prosemirror,bengler/prosemirror,tecnogram888/prosemirror,tzuhsiulin/prosemirror,kiejo/prosemirror