Problem
1. Add a function is_palindrome_letters_only to the Palindrome_Finder class that bases its findings only on the letters in a string (ignoring spaces and other characters that are not letters).
2. We showed how to implement a stack using a vector, which has an array as its underlying data structure. Assume that the STL container classes are not available and write a file Array_Stack.tc that implements a stack using an array for storage.