Added callback triggers for chunk upload events.

// Callback for the start of each chunk upload request:
chunksend: function (e, data) {}, // .bind('fileuploadchunksend', func);

// Callback for successful chunk uploads:
chunkdone: function (e, data) {}, // .bind('fileuploadchunkdone', func);

// Callback for failed (abort or error) chunk uploads:
chunkfail: function (e, data) {}, // .bind('fileuploadchunkfail', func);

// Callback for completed (success, abort or error) chunk upload
requests:
chunkalways: function (e, data) {}, // .bind('fileuploadchunkalways',
func);
Trigger a manual progress event when upload is done but loaded doesn't equal total uploaded bytes.