Introduce the concept of a DRC_PROVIDER which allows
to separate the various DRC functions to their own
areas. This allows, amongst other things, a slimmer core
DRC class, and allows DRC functions to be separately testable.
The courtyard DRCs (overlap, missing and malformed)
are the first victims, so instrumentation can be added to this function.
Add some unit tests on this DRC function, as well a few re-usable PCB-based
utility functions in a library (qa_pcbnew_utils) that could be shared between
unit tests and other utilities.
This separates the "newMarker" functions from the DRC class. These
are moved to a new class, DRC_MARKER_FACTORY, which is now responsible for
constructing suitable markers from BOARD_ITEMS.
The reasons for this are:
1) Allow DRC related functions to access theese functions without having
to bake these functions into the main DRC class.
2) Thereby simplify the DRC class interface
3) As DRC_MARKER is now a small class with public interfaces, it's
possible to put unit tests on these functions.
The motivation here is to allow to start to split out pieces of DRC
into separate classes.
John Beard