Row 0 being drawn at the bottom of the screen instead of top

[Jartza]

Pixels with y-coordinate at 0 are being drawn to the bottom of the screen (right before the bottom border) instead of top.

Easy to replicate:

cls(0):
line_draw(0, 0, 255, 0, 15);
line_draw(0, 1, 255, 1, 15);

I have opened a PR for a fix: #16