Implemented print keyword and associated tests

scripts/example-print.toy

@@ -0,0 +1,5 @@
+//print statement
+print 42;
+
+//it can handle complex expressions
+print 3 * 5;

scripts/example.toy

@@ -1 +1,2 @@
-(1 + 2) * (3 + 4);
+//expression
+(1 + 2) * (3 + 4);