grafx - Extensible Java Graphics Package Code

Changing little tidbits in CoveredHoleMetricUtils. Nearing completion.
Proofread but untested.

Moving canPlugHoleWithoutPlacingCubeAbove() to CoveredHoleMetricUtils, starting
to clean up CoveredHoleMetric.

Embellishing comments some more in CoveredHoleMetric.

Adding more examples for canPlugHoleWithoutPlacingCubeAbove().

Implemented canPlugHoleWithoutPlacingCubeAbove() in CoveredHoleMetric, but want
to proofread (and of course test eventually). Gave some examples in a comment.
Want to add at least one very complex example. Also in removed an irrelevant
comment.

Simplifying some indentation levels by removing 'else' blocks where possible.
CoveredHoleMetricUtils.java.

Starting to implement canPlugHoleWithoutPlacingCubeAbove() in
CoveredHoleMetric.

Finished the algorithm with the new x-ray technology. I need to proofread this
after a bit of rest. Completely untested. CoveredHoleMetricUtils.java.

Found a problem in the algorithm related to light rays vs. x-rays. Starting to
implement the fix. CoveredHoleMetricUtils.

Adding in the caching optimization. CoveredHoleMetricUtils won't check the
clearability of a single layer more than once.