In this assignment you will be writing a program to check for matched
parenthesis.  stacks have a function "empty" that describes if the
stack is empty or not. For example, if the stack, s, is empty, then
s.empty() is true. size is another popular function. Half of you will
use stacks and half will use vectors.


You should write a function that takes as an argument a string and
simply returns True or False (and then outputs MATCHED or UNMATCHED)
based on whether the symbols are matched or not. This string will
contain either parenthesis (), square brackets [], <> pairs and curly
brackets {}. Your program will examine the string to determine if the
symbols are matched appropriately.

Pseudocode for this is as we discussed in class:

For every symbol in the string,
   if it is not an open or close symbol
      then ignore it and move on to the next symbol
   if it is an open symbol: there are three ( [ { <
      push it on the stack
   if it is a close symbol, there are three ) ] } >
      check if the stack is empty
           if it is empty, then return false / output UNMATCHED  //sample input is ")"
      if the stack is not empty then check that then top matches the closed symbol    
           ) matches (, } matches {, ] matches [ and > matches <
	        if they match, pop that symbol off the stack
		     if they don't match, then return false / output UNMATCHED //sample input is "[)"

if all symbols have been examined, 
   then return true / output MATCHED if the stack is empty //sample input is "()" and ""
   and return false / output UNMATCHED otherwise //sample input is "(("