grafx - Extensible Java Graphics Package Code

Fixing a wrong increment for 'dd'.

In line drawing routines, changing cases of " += -value " to " -= value ".
It's much easier to follow and to copy this way.

Trying to handle one more type of line. Not culling pixel by pixel in the z
with existing line drawer.

Reverting back to clipping polygons along z axis in the post-normalized state.

Putting the line z-clipping in place. Getting a decent strategy in order.

Removing the drawLine() of varying color; simplifying the 3D graphics API and
comments.

Rearranging some stuff in RasterDepthGraphics.

Adding a comment and an explicit cast to NormalizeZ.

Adding random test cases to NormalizeZ, found no errors.

Refining some comments in RasterDepthGraphics.