I never remember using it, must be some ancient artifact.

Implement space:count() as a counterpart to space:len() for consistency
with space.index.

The new tarantool-python driver returns tuple from space
operations.

Remove ev_clear_pending(), which is already done by ev_io_stop().
Update comments.

Fix a subtle race condition in JOIN/SUBSCRIBE, a
pending event may be present against JOIN/SUBSCRIBE file
descriptor, in which case the descriptor could be resumed
in iproto thread concurrently with the relay thread.

No github issue, the case is repeatable by
running replication-py/cluster.test many times.

Implement box.cfg { read_only = true }

bool is_ro is now controlled by box.cfg{} and is not used by
register/unregister logic in _cluster table.

[documentation][skip ci]