Also, did the same thing for Die I did for DiePool, where I moved the
specific classes to the same file as the interface.

Also, changed my mind on the way DiePool and its implementations should
be structured. The implementations go in the die pool file as internal
classes, because nobody should particularly care the specifics about
their die pool, only that it does what it says it should

Renames several interfaces named in the IWhatever style, which Java
doesn't use

Convert dice from dealing exclusively with ints, to deal with objects of
arbitrary types