renderer/console: Implement line drawing

Now the console renderer can draw ASCII-lines!
renderer/console: Codestyle improvements

Some codestyle changes according to style +
add dots behind the documentation sentences.
renderer/console: Let DrawPoint() update z-buffer

DrawPoint() only checks whether it should be
rendered because it's in front of the z-buffer,
but doesn't update the z-value if it's really
not covered by other points.
renderer/console: Use Z-Buffer in DrawLine()

Z-buffer implemented in DrawLine() function.