Some docs and to_s testing

somewhat code_climate inspired

lib/ruby/send_statement.rb

@@ -1,5 +1,8 @@
 module Ruby
-
+  # Send and yield are very very similar, so they have a base class CallStatement
+  #
+  # The SendStatement really only provides to_s, so see CallStatement
+  #
   class SendStatement < CallStatement
     def to_s
       "#{receiver}.#{name}(#{arguments.join(', ')})"