Finding frequency of letters (50 points)
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The aim of this final assignment is have you do a  small number of
text-based tasks using the STL classes.

Your task is to input a text file, read through it, and determine
certain properties of the text.

A) Input:

For input, you are to take in a the filename as argument and open the
file as read-only.  You are welcome to use code from previous projects
in this, but this sort of thing should be old hat to you by now anyway.
I would recommend denoting input files using a ".txt" extension.

B) Processing:

You are to read the file in, and track the following statistics:
1) Letter frequencies
2) Frequency of initial and final letters per word



For example, for the words SIDE TABLE:
- The initial letters are S,T and the final are E,E
Upper and lower case alphabets should be treated as the same.

Reading in the file can be accomplished using getline() to obtain lines,
and then you can use "istringstream" to separate out the words.

I would recommend using a map<char, int> to track the letters.  
Make sure to ignore punctuation.  The main point is that you 
MUST use STL classes to implement these structures. 

C) Output:

Instead of outputting to standard output, you will be send the data to a 
file.  You will create the filename by replacing the ".txt" extension
from your input file with a ".out" extension.  For example, the output
for the file "quotes.txt" will be "quotes.out".  Make sure that the 
file is opened with writing (not appending) in mind.

The output in the file should have the three frequency tables in this
order: letter, initial, final.  You do not have
to sort the tables, but I will give extra credit (5 points) if you 
use the STL sort function to do it (even though I didn't really go over it in class).

For each table, I want: the thing your a giving the frequency for, 
the count, and the percentage of the total (the frequency).  For example,
last letter may look something like this:

Last-letter   Count     Frequency
---------    -----     ----------
D             15           33.5%
T             13           31.2%
...

Make sure everything is understandable.