Implement defining functions

Ycicle/Program.cs

@@ -29,6 +29,8 @@ namespace Ycicle
                 }
 
                 var parsed = new Script(input, variables);
+                Console.WriteLine(parsed.PrettyPrintSyntaxTree());
+
                 if (parsed.Diagnostics.Messages.Count > 0)
                 {
                     Console.ForegroundColor = ConsoleColor.Red;