message: Rename some variables
  `ReadUpTo` -> `RR`
  `ReadReceipt` -> `RR`
  `ReadMarker` -> `RM`
diff: @@ -507,10 +507,10 @@ var TimelinePanel = React.createClass({
  // if no client or client is guest don't send RR or RM
  if (!cli || cli.isGuest()) return;
  - let shouldSendReadReceipt = true;
  + let shouldSendRR = true;
  - const currentReadUpToEventId = this._getCurrentReadReceipt(true);
  - const currentReadUpToEventIndex = this._indexForEventId(currentReadUpToEventId);
  + const currentRREventId = this._getCurrentReadReceipt(true);
  + const currentRREventIndex = this._indexForEventId(currentRREventId);
  // We want to avoid sending out read receipts when we are looking at
  // events in the past which are before the latest RR.
  //
  @@ -524,33 +524,33 @@ var TimelinePanel = React.createClass({
  // RRs) - but that is a bit of a niche case. It will sort itself out when
  // the user eventually hits the live timeline.
  //
  - if (currentReadUpToEventId && currentReadUpToEventIndex === null &&
  + if (currentRREventId && currentRREventIndex === null &&
  this._timelineWindow.canPaginate(EventTimeline.FORWARDS)) {
  - shouldSendReadReceipt = false;
  + shouldSendRR = false;
  }
  const lastReadEventIndex = this._getLastDisplayedEventIndex({
  ignoreOwn: true,
  });
  if (lastReadEventIndex === null) {
  - shouldSendReadReceipt = false;
  + shouldSendRR = false;
  }
  let lastReadEvent = this.state.events[lastReadEventIndex];
  - shouldSendReadReceipt = shouldSendReadReceipt &&
  + shouldSendRR = shouldSendRR &&
  // Only send a RR if the last read event is ahead in the timeline relative to
  // the current RR event.
  - lastReadEventIndex > currentReadUpToEventIndex &&
  + lastReadEventIndex > currentRREventIndex &&
  // Only send a RR if the last RR set != the one we would send
  this.lastRRSentEventId != lastReadEvent.getId();
  // Only send a RM if the last RM sent != the one we would send
  - const shouldSendReadMarker =
  + const shouldSendRM =
  this.lastRMSentEventId != this.state.readMarkerEventId;
  // we also remember the last read receipt we sent to avoid spamming the
  // same one at the server repeatedly
  - if (shouldSendReadReceipt || shouldSendReadMarker) {
  - if (shouldSendReadReceipt) {
  + if (shouldSendRR || shouldSendRM) {
  + if (shouldSendRR) {
  this.lastRRSentEventId = lastReadEvent.getId();
  } else {
  lastReadEvent = null;
  