add a new field to the ABC Frame. The new field is a callback that may be called by a BMC-like engine when a frame is done and a PO is either known to be SAT or UNSAT up to a specific frame

main: allow the -c -C -q -f -F -s command line options to be repeated and the commands they sepcify be executed in order instead of overriding each other

make sure all of ABC and related libraries are in the same namespace (when compiled with ABC_NAMESPACE) by removing extern "C" from function definitions