Add config key SR_CONF_DIGITS.

include/libsigrok/libsigrok.h

@@ -1018,6 +1018,9 @@ enum sr_configkey {
 	/** The measurement range of a DMM or the output range of a power supply. */
 	SR_CONF_RANGE,
 
+	/** The number of digits (e.g. for a DMM). */
+	SR_CONF_DIGITS,
+
 	/* Update sr_key_info_config[] (hwdriver.c) upon changes! */
 
 	/*--- Special stuff -------------------------------------------------*/

src/hwdriver.c

@@ -197,6 +197,8 @@ static struct sr_key_info sr_key_info_config[] = {
 		"Logic threshold (custom)", NULL},
 	{SR_CONF_RANGE, SR_T_STRING, "range",
 		"Range", NULL},
+	{SR_CONF_DIGITS, SR_T_STRING, "digits",
+		"Digits", NULL},
 
 	/* Special stuff */
 	{SR_CONF_SESSIONFILE, SR_T_STRING, "sessionfile",