Fix a bug in simple diode, when ilimit is set, but not epsilon.

Make model more similar to LTSPICE
Add an example

examples/xspice/simple-diode.cir

@@ -0,0 +1,25 @@
+simple diode automatic test
+* 'set ngbehavior=lta'   required in .spiceinit
+V1 in 0 dc 0
+
+D1 in out1 A
+R1 out1 0 1u
+D2 in out2 B
+R2 out2 0 1u
+D3 in out3 C
+R3 out3 0 1u
+
+.probe alli
+
+.model A D(Ron=1 Roff=1Meg Vfwd=1 Vrev=2)
+.model B D(Ron=1 Roff=1Meg Vfwd=1 Vrev=2 Ilimit=1 RevILimit=1)
+.model C D(Ron=1 Roff=1Meg Vfwd=1 Vrev=2 Ilimit=1 RevILimit=1 epsilon=1 revepsilon=1)
+
+.control
+dc V1 -5 5 1m
+display
+set xbrushwidth=2
+plot i(r1) i(r2) i(r3)
+.endc
+
+.end

src/xspice/icm/xtradev/sidiode/cfunc.mod

@@ -147,23 +147,22 @@ void cm_sidiode(ARGS)  /* structure holding parms,
             grev = 1./PARAM(rrev);
 
         hRevepsilon = 0.5 * PARAM(revepsilon);
-        loc->Va = Va = Vrev - hRevepsilon;
-        loc->Vb = Vb = Vrev + hRevepsilon;
+        loc->Va = Va = Vrev - PARAM(revepsilon); //hRevepsilon;
+        loc->Vb = Vb = Vrev; //+ hRevepsilon;
+        loc->a2 = grev/Revilimit;
         if(hRevepsilon > 0.0) {
             loc->a1 = (goff - grev)/PARAM(revepsilon);
-            loc->a2 = grev/Revilimit;
             loc->revepsi = MIF_TRUE;
         }
         else
             loc->revepsi = MIF_FALSE;
 
         hEpsilon = 0.5 * PARAM(epsilon);
-        loc->Vc = Vc = Vfwd - hEpsilon;
-        loc->Vd = Vd = Vfwd + hEpsilon;
-
+        loc->Vc = Vc = Vfwd; // - hEpsilon;
+        loc->Vd = Vd = Vfwd + PARAM(epsilon); //hEpsilon;
+        loc->b2 = gon/Ilimit;
         if(hEpsilon > 0.0) {
             loc->b1 = (gon - goff)/PARAM(epsilon);
-            loc->b2 = gon/Ilimit;
             loc->epsi = MIF_TRUE;
         }
         else