This renames several interfaces that had names like IWhatever, since
that isn't a style that Java uses

IMap now returns optionals, instead of throwing an exception

Added a static function 'of' to IMap to allow you to more easily create
a map from a list of key-value pairs. However, misuse of this method can
result in getting ClassCastExceptions at some later point, because it
has to use Object var-args + an unsafe generic cast.

So, be careful, I suppose; and please make sure your argument types are
correct.

IMap has some default methods that its various implementations were
overriding when they didn't need to

Pass to do some cleanups

The package root is now bjc, not io.github.bculkin2442.