DataChannel.js — multiple files concurrent transmission supported

You can share more than one files simultaneously; without any failure or
lost; also; you can share multiple longest string messages concurrently
too.

Following demo now works fine on chrome too:

https://webrtc-experiment.appspot.com/part-of-screen-sharing/webrtc-data-channel/

You can detect messages latency too; as explained in issue #63:

channel.onmessage = function(message, userid, latency) {
—— console.log('latency:', latency, 'milliseconds');
};

"uuid" added to uniquely identify each file...

// show progress bar!
channel.onFileProgress = function (packets, uuid) {
—— // uuid is file unique identifier
};

"uuid" allows you show more than one progress bars; all progress bars
can be updated concurrently.

A bug in RTCMultiConnection-v1.4 is fixed; now multi-user connectivity
works fine; also "maxParticipantsAllowed".