Update CalculatorBrain.swift

Added an "AC" function, as well as a modulus ("%") function - in the calculator.swift I changed the layout as well, not sure if it was really wanted but got bored

Other Projects/Calculator/Calculator/Calculator/CalculatorBrain.swift

@@ -33,7 +33,9 @@ struct CalculatorBrain {
     "÷" : Operation.binary({ $0 / $1 }),
     "+" : Operation.binary({ $0 + $1 }),
     "−" : Operation.binary({ $0 - $1 }),
-    "=" : Operation.equals
+    "=" : Operation.equals,
+    "%" : Operation.binary({$0.truncatingRemainder(dividingBy: $1)}),
+    "AC" : Operation.constant(0)
   ]
   
   mutating func performOperation(_ symbol: String) {