removed section of deBracket code not required
(task 3a) modified enterPressed and operationPressed to update miniDIsplay with description of program
added deBracket code to fix up description in the case of 4 E 5 E + 3 E 4 E + = 4+5) + (3+4
added VariablePressed method and x,a,b buttons
added @property testVariableValues and getter
implemented setVariableDisplayToVariablesUsedInProgram
made testVariableValues strong as it was loosing it state between methods
removed getter
updated testVariablePressed to use doubles instead of strings for the values
UI changes
added variablesExistIntheProgram bool helper

clearPressed clears the variableDisplay and resets the variables
updateMiniDisplayVariablesToValues implemented by commented out for later use. don't think it is needed
implemented undoPressed and popOperandToDeleteFromProgram
moved ([self.display.text length] > 0) into display helper methods
refactored operationPressed - removed unnecessary code

added comments
added more comments
added +/- button and partial implementation
removed - (void)updateMiniDisplayVariablesToValues:(NSDictionary *)values