grafx - Extensible Java Graphics Package Code

Holy crapola I finally found an error case. It's some sort of error, I don't
know which.

Getting close to coming up with the error case.

Committing some commented-out println() statements in drawLinePosDxDy() which
explains the step-by-step process of pixel selection.

I am really struggling with this test code. Committing what I've got.

Adding a long comment regarding the possibility that an end pixel won't get
turned on.

Caching m_dx and m_dy in line drawing, 2D graphics.

Improving the degenerate line handling in 2D rendering.

Strarting to improve 2D line rendering code by removing extra checks that are
no longer necessary.

Adding comment block announcing experimental work in progress.

Adding new test code which exposes a bug: OnePixelSteepLine.