Add a simple GENSYM function

Resolves #18

src/function/builtin/GENSYM.java

@@ -9,10 +9,12 @@ import sexpression.*;
 public class GENSYM extends LispFunction {
 
     public static final String GENSYM_PREFIX = "#G";
+
     private static BigInteger counter = BigInteger.ZERO;
 
     private static Symbol generateSymbol() {
         incrementCounter();
+
         return new Symbol(GENSYM_PREFIX + counter);
     }