Caching in/with DataSet is broken

[mnlipp]

Nice library, thanks. Nevertheless, on a long running server, it needs more and more memory.

DataSet attempts to cache DataSet objects by nationality. However, Nationality does not define hashCode/equals. Thus we get a new entry for every newly generated object of type Nationality. And these objects are generated freely e.g. in Generator.generateRandomNationality. So each invocation of Generator.generateRandomUser effectively adds a DataSet to the cache that never goes away. And eventually, heap space is full, no matter how big it is.

[vatbub]

Hey, thanks for pointing that out. Unfortunately, I won't have time to fix this until next week, so, if you need an urgent fix, feel free to fork and make a PR.
Cheers