Add a variable to the system for capacitor currents. This seemingly s…

…mall change means that we don't need to solve for differentials before discretization, which may enable dynamic parameters to work! Partially addressing #94

Circuit/Components/Capacitor.cs

@@ -25,7 +25,7 @@ public static Expression Analyze(Analysis Mna, string Name, Node Anode, Node Cat
             V = Mna.AddUnknownEqualTo("V" + Name, V);
             // i = C*dV/dt
             Expression i = C * D(V, t);
-            //i = Mna.AddUnknownEqualTo("i" + Name, i);
+            i = Mna.AddUnknownEqualTo("i" + Name, i);
             Mna.AddPassiveComponent(Anode, Cathode, i);
             return i;
         }