jMe - Operator now understands how to apply itself to 2 operands.
jMe - Operand understands what are the valid operands in the system
jMe - Operands can be added. Added the '+' function to the operand
jMe - I dont think we need a private method now as code is readable
jMe - Should not be able to instantiate an invalid Operand. So making a class method avaliable for validation checks
jMe - Same for operator. Cannot instantiate an invalid operator
jMe - Support for multiplication as well
jME - Missing specs for operand arithmetic methods