Fixed a small defect in MutableCharDHashSO.findNewFreeOrRemoved: cleaned up unused local variable
Fixed bug in MutableCharDHashGO: common implementations of removeAll() and retainAll() for CharSet and Char*Map.KeySet should check the given collection is not identical to that sets, not MutableCharDHashGO instance itself, because in KeySet case MutableCharDHashGO is an outer map.
Added ability to check the code with FindBugs
Updated root README with a notice that Java 8 is required for the build