This implements a copper-layer RTree with functions for iterating over
the elements in a copper layer and providing Nearest Neighbor returns
for BOARD_CONNECTED_ITEMS
This moves EESchema DLIST structures to rtree. These changes are more
fundamental than the pcbnew changes from 9163ac543888c01d11d1877d7c1
and 961b22d60 as eeschema operations were more dependent on passing
drawing list references around with SCH_ITEM* objects.
* Split up the thirdparty code into the thirdparty folder (#3637)
* Create a new kimath static library containing all the math functions
This is part of cleaning the build system for #1906.
Seth Hillbrand
Mark Roszko
Ian McInerney