New arguments parser.

New arguments parser, designed to be configurable.  Automatically formats and prints Usage() for the user's terminal.  This version uses long option names ("--foobar") and works with both single options ("--frobulate") and key-value options ("--frobulate-with=fnord").  This should be suitable for reuse elsewhere in the code.

See `Runner#initArgs` for sample use.  The `Args` class is not strictly necessary; it just simplified some function calls.

Please let me know if you want this to work some other way.  I am open to suggestions.