Edge mode and moving selected vertex to drawing structure

- selected is now called v_selected and can be found in the drawing structure
- edge mode is implemented (except closestEdge function has to be done)
- TODO : Change the selected vertex/edge color
All the functions are implemented (but closestEdge gives shitty answers)

- drawing_rasterize paints selected edge or vertex in green
- middle clic in edge mode creates a new vertex selected and selected->next
- algorithm in closestEdge should be reviewed
Fixed some issues in closestVertex

...but some issues remain in closestEdge
Plot the last pixel with Bresenham

This is not important and may be reverted in the future. This patch is
only here for completeness and correctness.

Signed-off-by: Celelibi <celelibi@gmail.com>
Corrected some border errors when filling

The filling is still not always exact when the polygon is
self-intersecting, but it should be ok when it is simple enough.

Signed-off-by: Celelibi <celelibi@gmail.com>
Merge remote-tracking branch 'snqke-gh/master'
Indentation fixing

Bad whitespaces and bad indentation.

Signed-off-by: Celelibi <celelibi@gmail.com>
Sort lists of size 0

It's not an error to try to sort a list of active_edge with no element
at all.

Signed-off-by: Celelibi <celelibi@gmail.com>
Debugging horizontal edges

Horizontal edges were not handled properly because of some optimizations
that assumed they weren't. Now the removal and addition of an edge
adjacent to an horizontal edge is handled.

Still remain some bugs with very complex polygons.

Signed-off-by: Celelibi <celelibi@gmail.com>