#162 Units with higher powers in denominator cannot be formatted with UCUM formatter

[mattdehring]

This change is 

[frothga]

The change in UCUMFormat.java works for me. This is actually a pretty crucial bug. Please accept the request.

[keilw]

Do they depend on each other? Note, that #167 requires a Java 9 compliant clone of UCUMFormat, so whatever is applied in the default codebase also has to work there.

[frothga]

They don't depend on each other. IE: you don't need the static import change in order for the fix in UCUMFormat to work. And that fix in UCUMFormat is rather crucial. If you'd like a pull request for just that, I can put one in.

[keilw]

I check whether or not it's possible to create a 2.0.2 service release of Unit Systems based on the existing SI 2.0.1 release, there are too many planned features for 2.1 to do this very quickly, but the Jigsaw compliance of UCUMFormat must be guaranteed first, so both the Java 8 and Java9+ version must work.