Increase precision of arrows

[DarwinNE]

The rendering of arrows is not very precise as the segment is superposed to the tip.
With relatively large segment widths, this yields an ugly result, as follows:

This should be corrected.

[DarwinNE]

It should work for Bézier courbes, too!

[DarwinNE]

Of course, one must not forgot about splines (curves)... :-)

[DarwinNE]

I changed a little the style of the arrows from the version 0.24.7 so that they fit more what were my original intentions. This will change a little how the drawings are rendered, but in the vast majority of the situations, it will improve the drawings.

This code contains some (rather extreme) example of arrows:

[FIDOCAD]
FJC A 3.0
FJC B 3.0
LI 30 40 60 5 0
FCJ 3 2 14 8 0 0
CV 0 70 15 65 45 95 20 85 55 110 55 0
FCJ 3 3 14 8 0
BE 40 45 40 70 65 60 120 80 0
FCJ 3 2 14 4 0 0

This is the NEW result, with version 0.24.8:

Whereas this is the result with the version 0.24.7:

The changes are more evident with the empty arrows, but the geometry is the same for filled arrows, too. This means that the Bézier and spline curves change slightly of shape when they are traced with and without arrows.

[DarwinNE]

Now it remains to check the export towards all vector files supporting arrows: SVG, PDF, PGF, EPS 😭

[DarwinNE]

The implementation should be complete. Let's close this issue that required much more work than expected at a first sight.