CMPS 3600 Scott Troy Lab 11

This program will be used to add or remove access permissions to different 
groups on specified files.

It will be compiled from its source file by the following:

    gcc -Wall Scott_Troy_Lab11.c -omychmod
    
The program 'mychmod' accepts multiple command-line arguments by user input.
An example of how it will be executed at the command-line:

    ./mychmod -u rwx a.out
    
Valid flags are [u, g, o, U, G, O], each followed by any permutation of [r, w, x].
All file names must be included at the end of the command.

The three lower-case flag-options will add specified permissions to all of the
files listed at the command-line.

The flags represent different access groups, as follows:
    
    -u : user add permissions
    -g : group add permissions
    -o : others' add permissions
    -U : user remove permissions
    -G : group remove permissions
    -O : others' remove permissions
    
The options following a flag are as follow:

    r : read permission
    w : write permission
    x : execute permission
    
NOTE:

This program allows the current user to modify permissions on files he/she
has created; it will not allow modification to permissions of files they do not own. 

The program must use only any of the six permission flags and the required 
three options to either grant or remove permissions for a file. Errors will
occur otherwise.

If no file is provided, an error will occur and the user will be asked to check
his/her arguments.

If multiple files are included, only the valid ones will have their permissions updated.
An error message will still be displayed after execution terminates, however.