Leaky bucket implementation ported from nginx

Theory

See /doc (TODO)

Usage

Set up limits

zone = Zone('zone_name', rate_limit)
limit1 = Limit(zone, burst, nodelay)

Default zones

TODO

Decorators

@limit_calls(zone, burst, nodelay)
def some_function():
    """Usage with non-awatables"""
    return 0


@limit_calls(zone, burst, nodelay)
async def some_other_function():
    """Usage with awatables"""
    return await asincio.sleep(1)

Manual mode

(Not implemented yet)

Transform a table with calls:

    (timestamp, requester_id, requested_object)

Into

   (timestamp, requester_id, access_granted, delay, excess)

Synchronous mode

TODO