grafx - Extensible Java Graphics Package Code

Adding long comment describing a problem with the covered hole metric.

Exposes a problem with the computer player.

Revising data/excellent-computer-player.blo.

Changing the well colors slightly.

Carrying over the changes done to SinglePlayerLevelAction, with respect to
setting next block to null when level is finised, in ComputerPlayerLevelAction.

Removing commented out code block that was instrumenting the BlockSource, for
purposes of testing the covered hole metric. Using GamestateListenerChain and
LevelFinishedCausesNullNextBlock to set next block to null when level is
finished. These little changes really make the game seem more polished.

Adding class LevelFinishedCausesNullNextBlock.

Altering documentation a little bit.

Adding DummyGamestateListener.

Finished implementing all levels 1 through 24, inclusive. I think this will
be enough. Default computer level changes to 21 (because the level number
changed as well). Orange and white color flip in game text, to encourage
viewing white stuff.