Argument Converters

Converters to use with parser configurations like:

parser.accepts("p").withRequiredArg().withValuesConvertedBy(new OnlinePlayerValueConverter()).describedAs("Player to teleport to");

Adds the following converters:

- OnlinePlayerValueConverter - converts to an online player of the same name
- CoordinatesValueConverter - converts x,z or x,y,z into a coordinates object (worldless)
- LocationValueConverter - converts world,x,z or world,x,y,z into a Location object