This places the arc approximation setting in the kicad_pcb file and uses
it for all parts of the board rendering where arcs are converted to
segments. This allows the user to customize their speed vs. accuracy
tradeoff. The default setting of maximum error of 0.005mm is acceptable
for small boards on moderate systems.
This corrects an issue with fill segments-per-circle and moves the error
to segmetns calculation down in a number of functions to expose the
single value for approximation
Allows 0 to 4 chamfered corners, not only one.
A custom shape allow this kind of shape. However because it is a primitive,
it is easier to edit and it support thermal reliefs.
* Specctra exported polygons are now closed (as required)
* export custom shape is provided in code, but not activated, because i have no way to text it
* fix Specctra export dialog (replace OK and Cancel buttons by only one Close button)