Added (somewhat rudimentary) support for file ranges.  Users can pass single files exactly as before, but they can also now pass ranges of filenames. For example: ipg111127-ipa121204.zip gets all the patent grants between those dates.  This example also illustrates some of the shortcomings with the current implementation.  ipg111127.zip is not actually a file, which is fine behaviorally, but may confuse users.  Additionally, the prefix of the second filename does not matter.  It is stripped out and ignored.  However, some sort of warning should be put in place if the user attempts to pass a range with different patent types.