grafx - Extensible Java Graphics Package Code

Finished refactoring the line drawing code for constant color.

Moving xx, yy, and inx local variable definitions out of the four constant
color line drawing routines, into the parent function, passing them as input
parameters.

Paving the way for refactor of the constant color line drawing code.

Streamlining some more of the color interpolated line drawing code; instead of
explicit zMin and zMax, using the arrays m_zargbMin & m_zargbMax.

Preliminary attempts at NEW_BLOCK_POSITIONING_STRATEGY_CENTERED. I want to
send the even cases to +0.5 as well, I think that will work better.

Nightmare mode gets center placement strategy.

Adding some infrastructure to properly shade the line colors.

The block drop (system) speed after speedups is now about to go faster than
half the speed of the user drop events; the millis per system drop reached a
minimum of twice the millis for user drop, and now it's set to 1.5x instead of
2x. So it drops faster after speedups.

Adjusting nightmare level a little bit.

Speeding up millisUserDropInterval just a hair.