grafx - Extensible Java Graphics Package Code

Implemented the three layers cleared bonus strategy but I'm not so sure that it
works, yet.

Making incremental changes to incentivize the clearing of three or more layers
at once. For now added new field in inner class BlockPlacementStrategy.Move,
named 'threePlusLayersCleared'. Reduced SUPERMAXIMAL_EVAL_SCORE to 10.4
because we're expecting to define THREE_LAYERS_CLEARED_SCORE_BOOST as 0.3, and
the sum of the two will be 10.7, which is still allowable.

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.