timevar: document in the header, not in the implementation

* lib/timevar.c: Move documentation from here...
* lib/timevar.h: to there.

lib/timevar.h

@@ -75,12 +75,46 @@ typedef enum
 timevar_id_t;
 #undef DEFTIMEVAR
 
+/* Initialize timing variables.  */
+
 void timevar_init (void);
+
+/* Push TIMEVAR onto the timing stack.  No further elapsed time is
+   attributed to the previous topmost timing variable on the stack;
+   subsequent elapsed time is attributed to TIMEVAR, until it is
+   popped or another element is pushed on top.
+
+   TIMEVAR cannot be running as a standalone timer.  */
+
 void timevar_push (timevar_id_t);
+
+/* Pop the topmost timing variable element off the timing stack.  The
+   popped variable must be TIMEVAR.  Elapsed time since the that
+   element was pushed on, or since it was last exposed on top of the
+   stack when the element above it was popped off, is credited to that
+   timing variable.  */
+
 void timevar_pop (timevar_id_t);
+
+/* Start timing TIMEVAR independently of the timing stack.  Elapsed
+   time until timevar_stop is called for the same timing variable is
+   attributed to TIMEVAR.  */
+
 void timevar_start (timevar_id_t);
+
+/* Stop timing TIMEVAR.  Time elapsed since timevar_start was called
+   is attributed to it.  */
+
 void timevar_stop (timevar_id_t);
+/* Fill the elapsed time for TIMEVAR into ELAPSED.  Returns
+   update-to-date information even if TIMEVAR is currently running.  */
+
 void timevar_get (timevar_id_t, struct timevar_time_def *);
+
+/* Summarize timing variables to FP.  The timing variable TV_TOTAL has
+   a special meaning -- it's considered to be the total elapsed time,
+   for normalizing the others, and is displayed last.  */
+
 void timevar_print (FILE *);
 
 extern int timevar_report;