merge: only store one direction of copies in the copy map
simplify checkpair
generate copied hash from copy map
make copy cases more symmetrical
adding dir/bar
adding foo
dir/bar
foo
adding dir/bar_2
adding foo_2
dir/bar_2
foo_2
adding a
adding c
adding b
adding d
removing a
removing c
recording removal of a as rename to b (100% similar)