Property is a pad info used mainly for fabrication or test.
Currently, supported properties are:
BGA property (variant of SMD pad)
Fiducial (global to the board or local to the footprint)
Test Point
Heat sink
Castellated.
And are used in Gerber files (copper layers and drill files)
Increment BOARD_FILE_VERSION to 20200104
The pin name defined in Eeschema is now available as pad info.
Useful for the board designer (the pin function is displayed in the message panel).
Needed for the Gerber P&P files.
Oblong holes (slots) use now a aperture attribute similar to round holes.
(The previous attribute "slot" is now deprecated)
However they have a specific aperture, and a comment is added in drill files for these apertures.