Add a "--gauge" option which alters the progress bar to show the current rate as a percentage of the max rate seen, if the size is unknown (#46).

src/include/options.h

@@ -66,6 +66,7 @@ struct opts_s {
 	bool cursor;                   /* whether to use cursor positioning */
 	bool numeric;                  /* numeric output only */
 	bool wait;                     /* wait for transfer before display */
+	bool rate_gauge;               /* if size unknown, show rate vs max rate */
 	bool linemode;                 /* count lines instead of bytes */
 	bool null_terminated_lines;    /* lines are null-terminated */
 	bool no_display;               /* do nothing other than pipe data */

src/include/pv-internal.h

@@ -123,6 +123,7 @@ struct pvstate_s {
 		bool cursor;                     /* use cursor positioning */
 		bool numeric;                    /* numeric output only */
 		bool wait;                       /* wait for data before display */
+		bool rate_gauge;                 /* if size unknown, show rate vs max rate */
 		bool linemode;                   /* count lines instead of bytes */
 		bool bits;			 /* report bits instead of bytes */
 		bool decimal_units;		 /* use decimal prefixes */

src/include/pv.h

@@ -183,6 +183,7 @@ extern void pv_state_show_stats_set(pvstate_t, bool);
 extern void pv_state_numeric_set(pvstate_t, bool);
 extern void pv_state_wait_set(pvstate_t, bool);
 extern void pv_state_delay_start_set(pvstate_t, double);
+extern void pv_state_rate_gauge_set(pvstate_t, bool);
 extern void pv_state_linemode_set(pvstate_t, bool);
 extern void pv_state_bits_set(pvstate_t, bool);
 extern void pv_state_decimal_units_set(pvstate_t, bool);