缺少BITFIELD命令

[luoyunchong]

https://redis.io/docs/latest/commands/bitfield/

[2881099]

提交代码了，没来得及测试，API这样设计不知道是否灵活。

long[] results = cli.BitField(key, 
new BitFieldAction { BitFieldOperation.get, new object[] { "encoding", offset } },
new BitFieldAction { BitFieldOperation.set, new object[] { "encoding", offset, value } },
new BitFieldAction { BitFieldOperation.incrby, new object[] { "encoding", offset, increment } },
new BitFieldAction { BitFieldOperation.overflow_sat },
);