Add feature to change currency to GBP

src/currencyExchange.c

@@ -6,3 +6,10 @@ float toUSD(float euro) {
 
     return USD;
 }
+
+float toGBP(float euro) {
+
+    float GBP = euro * CURRENT_GBP_RATE_OF_ONE_EURO;
+
+    return GBP;
+}