The following mixin methods aid in the retrieving of information from the command line.
True if long begins with the characters from short.
Get all gem names from the command line.
Get the single gem name from the command line. Fail if there is no gem name or if there is more than one gem name given.
Get a single optional argument from the command line. If more than one argument is given, return only the first. Return nil if none are given.
[Validate]