Document classes and member variables unless obvious

Author: Owen Jones

CODING_STANDARD.md

@@ -77,6 +77,8 @@ Formatting is enforced using clang-format. For more information about this, see
   ///   function. For out-parameters, use "\param [out]".
   return_typet my_function(argt arg_name, argt &long_arg_name)
   ```
+- Classes and member variables should also be documented using the above format
+  when it is not immediately obvious what they do. 
 - The priority of documentation is readability. Therefore, feel free to use
   Doxygen features, or to add whitespace for multi-paragraph comment blocks if
   necessary.