grafx - Extensible Java Graphics Package Code

Fixing the FloatPolyClipper with a boundary condition which would lead to
NullPointerException. It seems like a harmless change but it has a huge
impact in very specific cases. This change had already been made to blockout
project, and is tested. Just rolling the fix into this repo. Some benign
comment changes, and benign debug method additions as well.

Adding a comment to BlockGenerator.

Fixing net.blockout.meta.BlockGenerator to name the 1-unit block "O" instead of
"_", the previous name was causing a compile error. It used to work with
Java 1.0, Java 1.1, even with Java 1.2, but apparently not anymore. This
generator now creates a carbon copy of the source file for
net.blockout.production.Blocks, so that source does not need to be adjusted.
It was already adjusted by hand a while back.

Adding a new constructor to PlaybackCanvas which takes a NextBlockListener.

Adding TODO comment to SynchronizedModeGamePlayback.

Adding NightmareLevelPlayback. Still working on it.

Adding DummyUserInput.

Showing how to use NextBlockListener with the playback.

Making a first pass at the NewBlockStartsEvent logic. It's complete but
untested.

Making incremental progress towards the NextBlockListener logic in
SynchronizedModeGamePlayback.