rectangle - Draws a rectangle

Draws a rectangle (graphics mode)

Gets: Left, Top, Right, Bottom

(left,top) is the upper left corner of the rectangle, and (right,bottom) is
its lower right corner.

Returns: On r0: 0 on success, -1 on failure

Example:

.text

.word 0

calls $0, .initgraph

pushl $10

pushl $490

pushl $390

calls $4, .rectangle