introduce qd as an alias for diode charge to get the right unit in plotting

examples/various/diode_ac_par.sp

@@ -18,11 +18,11 @@ d1 1 0 myd
 + IBV = 10u)
 
 .control
-save @d1[gd] @d1[cd] @d1[charge]
+save @d1[gd] @d1[cd] @d1[qd]
 dc v1 -5 .1 0.01
 plot @d1[gd]
 plot @d1[cd]
-plot @d1[charge]
+plot @d1[qd]
 .endc
 *
 .END

src/spicelib/devices/dio/dio.c

@@ -27,6 +27,7 @@ IFparm DIOpTable[] = { /* parameters */
  OP("gd",   DIO_CONDUCT,IF_REAL, "Diode conductance"),
  OP("cd",   DIO_CAP, IF_REAL, "Diode capacitance"),
  OPU("charge", DIO_CHARGE, IF_REAL, "Diode capacitor charge"),
+ OPR("qd", DIO_CHARGE, IF_REAL, "Diode capacitor charge"),
  OPU("capcur", DIO_CAPCUR, IF_REAL, "Diode capacitor current"),
  OPU("p",      DIO_POWER,  IF_REAL, "Diode power"),
  OPU("sens_dc",DIO_QUEST_SENS_DC,     IF_REAL,   "dc sensitivity "),