Demonstrate how to dynamically add variables to an object (a class instance) at runtime.

This is useful when the methods/variables of an instance are based on a data file that isn't available until runtime. Hal Fulton gives an example of creating an OO CSV parser at An Exercise in Metaprogramming with Ruby. This is referred to as "monkeypatching" by Pythonistas and some others.

   C=:<'exampleclass'         NB. this will be our class name
   V__C=: 0                   NB. ensure the class exists
   OBJ1=:conew 'exampleclass' NB. create an instance of our class
   OBJ2=:conew 'exampleclass' NB. create another instance
   V__OBJ1,V__OBJ2            NB. both of our instances exist
0
   W__OBJ1                    NB. instance does not have a W
|value error
   W__OBJ1=: 0                NB. here, we add a W to this instance
   W__OBJ1                    NB. this instance now has a W
0
   W__OBJ2                    NB. our other instance does not
|value error