Support for JDK 9 modules

[jonatino]

Noticed the main pf4j has support for jigsaw modules using module-info.java. Can we get that added here as well?

[decebals]

As you see in pf4j/pf4j#405, the problem is not solved entirely.
It's a problem with JSemVer. For more details see pf4j/pf4j#426.

[decebals]

@jonatino Can you create a MR?