line - draws line
line draws a line between two specified points.
line draws a line from (x1, y1) to (x2, y2) using the current color.
Gets: x1, y1, x2, y2 on stack.
Returns: On r0 - 0 on success, -1 on error
Example:
.text
.word 0
calls $0, .initgraph
pushl $0
pushl $0
pushl $720
pushl $424
calls $4, .line