AUTHORS.txt: add some contributor names (I certainly forgot some other contributors, and I apologize).
Demos: convert .brd files to .kicad_pcb files and fix 2 broken files

* A track is seen connected to a pad if the track end is inside the pad shape.
* Pads inside pads are now seen connected, if the center of the pad is *inside* the other pad.
* this is made to be sure a large copper area is shared by the 2 pads,  and to keep algorithm fast.