Implement detection of circles

[Aypac]

Find a way to detect simple circles and replace those polygons with the according TikZ command.

If the gds is created directly by gdspy commands one can detect the use of the Round class and use the original creation parameters ( see https://github.com/heitzmann/gdspy/pull/51 ).

from the gdspy docs:

Examples
--------
>>> circle = gdspy.Round((30, 5), 8)
>>> ring = gdspy.Round((50, 5), 8, inner_radius=5)
>>> pie_slice = gdspy.Round((30, 25), 8, initial_angle=0,
...                             final_angle=-5.0*numpy.pi/6.0)
>>> arc = gdspy.Round((50, 25), 8, inner_radius=5,
...                       initial_angle=-5.0*numpy.pi/6.0,
...                       final_angle=0)

(From discussions with Marc)

If loaded from a file, one can test each polygon if it is a circle, arc, pie slice, ring or ring slice:

For each polygon in a polygon set (with 2 or less polygons):
  go over each polygon and calculate the distance between neighbouring points
  If they are all equal (enough):
    it is a circle
  elif they are all equal (enough), except for one:
    it is an arc

Some more thoughts:

• You can do 250.000 distances per second on my pc for example
• I would put this on a flag anyway and if it causes trouble, you can just switch it off
• As soon as two distances are not the same, you can stop calculating distances for that array (So unless a polygon starts with something resembling a circle, it will probably only check the first few points)
• how about tolerances? Depends on the amount of digits that is written away. But quite small.
• set a flag with the minimum amount of points in an array to start doing this process, as a square is also a regular polygon.

[Aypac]

The discussion at heitzmann/gdspy#51 has resulted in a negative reply (I agree that it does not make sense to implement it there). The reason for this is ofc to reduce the number of polygons and therefore filesize greatly.