BBT_Time: provide conversion to/from integer format

This is not guaranteed to be lossless, but with 44 bits for bars,
256 beats per bar and up to 4095 ticks per beat, it should be fine.

libs/temporal/bbt_time.cc

@@ -23,6 +23,24 @@
 
 using namespace Temporal;
 
+int64_t
+BBT_Time::as_integer () const
+{
+	/* up to 256 beats in a bar, 4095 ticks in a beat,
+	   and whatever is left for bars (a lot!)
+	*/
+	return (((int64_t) bars)<<20)|(beats<<12)|ticks;
+}
+
+BBT_Time
+BBT_Time::from_integer (int64_t v)
+{
+	int32_t B = v>>20;
+	int32_t b = (v>>12) & 0xff;
+	int32_t t= v & 0xfff;
+	return BBT_Time (B, b, t);
+}
+
 BBT_Time
 BBT_Time::round_up_to_bar() const
 {