Rewrote the argument parsing to use argparse
Also:
 - Various PEP 8 fixes:
   - class names should start with a capital letter
   - indentation is spaces instead of tabs
   - comparisons with None are now the correct form: "is None" or "is not None" instead of "== None" or "!= None" respectively
   - string formatting uses str.format(); obviates AzCmd._parse_modification_time
   - added spaces after commas for method argument lists where missing
   - added spaces before and after arithmetic operators where missing
   - removed unnecessary trailing whitespace
   - removed unnecessary whitespace from blank lines