cmMidiFile.h : Added comments.

cmMidiFile.h

   {
     unsigned                   uid;     // uid's are unique among all msg's in the file
     unsigned                   dtick;   // delta ticks
-    unsigned                   atick;   
+    unsigned                   atick;   // accumulated ticks
     cmMidiByte_t               status;  // ch msg's have the channel value removed (it is stored in u.chMsgPtr->ch)
     cmMidiByte_t               metaId;  //
     unsigned short             trkIdx;  //