Remove CheckedConsumer. Added BooleanSupplier.

These still aren't in use, but I'm steering towards how this
is done in Java 8. Stream.forEachUntilCancelled() takes a
Consumer and a BooleanSupplier to indicate a break in internal
iteration. Let's do the same. (CheckedConsumer was problematic anyway).
Let's put a newline at the end of our XML files.