Add java modularity support

[loic-prieto]

Hi, Fabrizio!

I'm a very happy user of your library, thanks for all the work you've put into it!

As I'm looking to migrate to my application to java 11, I'm trying to modularize it in order to be able to make a java custom image (with jlink), so that I can distribute it more easily and in a compact maner.
In order to be able to create a custom image, all the dependencies must be "official" java modules, not any auto-modularized can exist (that is, if you do not specifically convert your jar to a java module, all libraries are transformed into an auto-modularized library).

I'm acutely aware that the migration effort to convert a library into a java module is highly variable depending on how much work you want to put into it, and how many dependencies you're using, and the modularization of the library itself. It is not only a matter of putting modules-info.java and call it a day.

So, I think everyone would benefit from this effort, if you're willing to do it. Would be very nice!

Thanks again for maintaining the library!

For reference, I'm using it to build a 4X framework, at https://github.com/loic-prieto/4xframework .