support multi-mode CLI interfaces

[lexicalscope]

Allow nested CLI definitions so options can be grouped depending on the mode of the application - the master option would control the availability of the slave options:

interface Top {
@option SlaveOne getSlaveOneOption();
boolean isSlaveOneOption();

@option SlaveTwo getSlaveTwoOption();
boolean isSlaveTwoOption();
}

interface SlaveOne {
@option getMandatorySlaveOneOption()
}

etc...

[darnells]

Multi-mode support would be very useful to my current project. I would be happy to help test the feature when it is implemented.