* new bulk rmw: intersection, intersection_negate (with complement),
* new bulk reads: empty, full, count, count_intersect
* ck_bitmap_iterator fixes: avoid out of bounds read on empty bitmaps,
and ck_bitmap_next is marginally faster on sparse bitmaps .
* less space: the bitmap itself is an array of unsigned int, which
eliminates alignment padding between the n_bit field and the bitmap.
* more unit tests.
This changes comes at the cost of clear linearizability, which
is suitable for my use-case. Users can easily implement linereazability
through an additional level of indirection to the ck_bitmap object.