fix #15, default toString for a class

+default comparison for a class
!give up struct in favor of class (simpler)

docs/declaring_arguments.md

@@ -1,7 +1,7 @@
 # Declaring arguments in Lyng
 
 It is a common thing that occurs in many places in Lyng, function declarations, 
-lambdas, struct and class declarations.
+lambdas and class declarations.
 
 ## Regular