PathExpander helps pre-process command-line arguments expanding
directories into their constituent files. It further helps by
providing additional mechanisms to make specifying subsets easier
with path subtraction and allowing for command-line arguments to be
saved in a file.
NOTE: this is NOT an options processor. It is a path processor
(basically everything else besides options). It does provide a
mechanism for pre-filtering cmdline options, but not with the intent
of actually processing them in PathExpander. Use OptionParser to
deal with options either before or after passing ARGV through
PathExpander.