grafx - Extensible Java Graphics Package Code

In levels 21 & 22, changing height of pit (z value) from 10 to 11. More space
in case the block sequence is unfavorable by chance, so there's more room to
recover.

Adding 'very-tricky.blo'.

Fine-tuning level 21.

Adding 'excellent4.blo'.

Minor adjustments on some of the new levels.

Adding 'excellent3.blo'.

Swapping levels 21 and 22, based on difficulty.

Adding a new level 22.

Adding a new level 24.

Adding a new level 23, which is a 3x3 pit with hard blocks. Bumping prior
levels 23-25 up by one.