doc: update todo list
lib/tree: rename branch_assert_parenthood to branch_paternalize
lib/tree: if was_root, don't bother setting this->hdr.prev
lib/tree: use 0, not NULL, for node references
lib/tree: tweak leaf_half down slightly
lib/tree: use leaf_data_ptr in leaf_xfer_half
lib/tree: tweak leaf_half a bit more
lib: remove alignment, message from dump_mem
test: fix erroneous use of PRId32 on uint32_t
lib/tree: fix erroneous use of PRId* on uint*_t