jmod usage info, and suggestions

[Jonathan Gibbons]

Here's jmod's usage output:

> usage: jmod config [<module-id> ...]
>        jmod create [-L <library>] [-P <parent>]
>        jmod dump <module-id> <class-name>
>        jmod identify
>        jmod install <classes-dir> [-r <resource-dir>] <module-name> ...
>        jmod list [-v] [-p] [<module-id-query>]
>        jmod preinstall <classes-dir> <dst-dir> <module-name> ...
>        jmod reindex [<module-id> ...]
>        jmod show <module-id>

Note, in particular, it uses <classes-dir> in a couple of places. It is 
not clear from the context whether this is a "typical" classes directory 
(e.g. build/classes) containing a single module, or a new "modules" 
directory, with an extra level of naming before getting to the package 
hierarchies.  Going forward, there is the potential for an ongoing 
source of confusion here, so we should try and come up with terminology 
to distinguish these cases, and we should then be careful to use it 
consistently.

I believe the current version of jmod expects <classes-dir> to be a 
modules directory.

A common case may be for folk to compile their code as a single module, 
so they will likely compile to build/classes, not build/modules.  Maybe 
jmod could detect this, by checking for <classes-dir>/module-info.class 
or <classes-dir>/*/module-info.class.

-- Jon