% Makes a string unique in strings by appending a number
%
% If str is part of given strings, function appends the smallest
% integer >= 1 to str, so that the new string is not part of the
% string list.
% If str is is not part of given strings, function returns str.
%
% Inputs
%   str - The string to make unique as char array.
%   strings - The string list as cellstr.
%   separator (optional) - A char array that separates str from the number
%                          appended.
%
% Outputs
%   uniqueStr - The new unique string.
%
% Examples
%   >> makeUnique('foo', {'foo', 'foo1', 'bar'})    % ans = 'foo2'
%   >> makeUnique('peter', {'paul', 'steve'})       % ans = 'peter'
