Add support for COUNT option in SCAN and its families about asyncio-redis HOT 6 CLOSED

#! /usr/bin/env python3

import asyncio
import asyncio_redis as aioredis

@asyncio.coroutine
def go():
    print('asyncio_redis at {}'.format(aioredis.__file__)) # Installed using "setup.py develop"
    print('connecting')
    conn = yield from aioredis.Pool.create(host='192.168.59.103', port=6379)
    print('begin')
    cur = yield from conn.scan('*')
    cur.count = 1
    fet_count = 0
    while True:
        cur.count += 0  # <-- I have changed this value from 0 to 5
        v = yield from cur.fetchone() # Inside, I printed "----" before calling _fetch_more()
                                      # and the number of items fetched per iteration is
                                      # approximately same to the given count.
                                      # Please note that the count is just a hint, and
                                      # the actual number of fetched items may differ.
        if v is None: break
        print(v)
        fet_count += 1
    print('end, fetched {} items'.format(fet_count)) # the result is consistent
    conn.close()

if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(go())
    loop.run_until_complete(asyncio.sleep(0))
    loop.close()