grafx - Extensible Java Graphics Package Code

Adding TODO.txt having to do with giving bonuses when three or more layers are
cleared at once.

Some minor modifications to comments in BlockPlacementStrategy.

Improving Javadoc, taking care of some small fiddly bits in the code, removing
some calls to clear() which are not needed (related to garbage collection). It
is anticipated that these changes will have no effect on the computer player.

In BlockoutConstants, shorting millisMultiClearSpacing and
millisUserDropInterval just a tiny bit.

In BlockPlacementStrategy.getNBestMoves() (the meat and potatoes of that class)
starting lesserIndex from 0xffffffff instead of the old 0x7fffffff. We can
use the high bit because within the long key the bits find themselves in the
lower 32, so they don't interfere with proper ordering of the long keys.
I checked the code and the keys themselves are not use anywhere; only their
order is important.

Removing from TODO.txt file the items that have already been done.

Fixing BlockPlacementStrategy, so that it chooses a quick end-of-level move
instead of continuing on and on. I still want to go through this and proofread
it, but after testing it definitely is working in the general case.

Changing millisBlkMvTime from 200 to 210 milliseconds in BlockoutConstants.

Trying to add some end-level logic which hurries up and clears the last layer
to finish a level. Right now this definitely isn't working; something is
terribly wrong, but I am running out of time to make the commit. So this is a
commit to bring it to a not-working state, with most of the code having been
modified to achieve this result.

Fixing ImmediateModeGamePlayback to include NEXT_BLOCK_AFTER_FIN type events
when generating a BlockSource.