create fast set type

[ramwin]

the fast set type will create a cache in memory. It's 20x faster the the redis set.

[#20#wangx@manjaroamd:hot-redis (fast_set)] $ python3 -m unittest discover tests
INFO:test_types:task 0 use DelayBuyFastSet: 0.003921, result: 1667
INFO:test_types:task 3 use DelayBuyFastSet: 0.003925, result: 1667
INFO:test_types:task 1 use DelayBuyFastSet: 0.003921, result: 1667
INFO:test_types:task 2 use DelayBuyFastSet: 0.003853, result: 1667
INFO:test_types:task 0 user redis directly: 0.076120, result: 1667
INFO:test_types:task 1 user redis directly: 0.073611, result: 1667
INFO:test_types:task 3 user redis directly: 0.078494, result: 1667
INFO:test_types:task 2 user redis directly: 0.076143, result: 1667
.
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Ran 1 test in 0.374s

OK

[ramwin]

@stephenmcd Could you review this pull request during your spare time?