DPM Direct Part Marking Support

[mdostalik]

libdmtx is optimized for square dots and not round dots (DPM). Would be nice to know the parameters necessary to successfully decode DPM format.

[toktarov84]

OPENCV open erode
https://docs.opencv.org/3.4/db/df6/tutorial_erosion_dilatation.html
https://docs.opencv.org/3.4/d3/dbe/tutorial_opening_closing_hats.html