title: How to generate a list of all possible strings from shortest to longest
body: <p>I need to generate an infinite list of strings using numbers and letters.  The first string should simply be "a", then "b" through to "z", then "0" through to "9", then "aa", "ab" etc.</p>
  
  <p>I can easily generate the ones with one character, but then it gets more complicated.</p>