Filter dense lines on curved surfaces

[osresearch]

As demonstrated in @level2three's tweet, curved surfaces end up with very dense numbers of line segments.

stl.min_length = 10; reproject=1

seems to produce reasonable results.

[osresearch]

Example with 10 versus the old default of 1.

[osresearch]

5 seems like a good compromise. merged in https://github.com/osresearch/plotter-vision/commit/84da4923c2b02eec44f141bf0fec6a19e950443e