Add subcommand class

eg.

@SubCommand(value = "sub", parent = ParentCommand.class)
public class SubCommandClass extends AnnotatedCommandExecutor<SamplePlugin> {

}

will result in /parent sub ...

Ok, it went far way...

@BaseCommand ()									/command
- @SubCommand("test1") ()						/command test1
- @SubCommand("test2") (World world)			/command test2 world
- @SubCommand("test3") ()						/command test3
- - @SubCommand("test3test1") ()				/command test3 test3test1
- - @SubCommand("test3test2") (World world)		/command test3 test3test2 world
- @SubCommand("test4") (World world)			/command test4 world
- - @SubCommand("test4test1") ()				/command test4 world test4test1
- - @SubCommand("test4test2") (World world)		/command test4 world test4test2 world

@BaseCommand (World world)						/command world
- @SubCommand("test1") ()						/command world test1
- @SubCommand("test2") (World world)			/command world test2 world
- @SubCommand("test3") ()						/command world test3
- - @SubCommand("test3test1") ()				/command world test3 test3test1
- - @SubCommand("test3test2") (World world)		/command world test3 test3test2 world
- @SubCommand("test4") (World world)			/command world test4 world
- - @SubCommand("test4test1") ()				/command world test4 world test4test1
- - @SubCommand("test4test2") (World world)		/command world test4 world test4test2 world