Add command "BITPOS" introduced on Redis 2.8.7

Redis 2.8.7 release note : antirez/redis@464fef9

Redis 2.8.7 introduces BITPOS command.
It finds first position of bit (0 or 1) from string value.
Usage is "BITPOS key bit [start] [end]", with start and end range is "byte" range, not "bit" range.

More descriptions on http://redis.io/commands/bitpos

* make apis to Jedis, BinaryJedis, PipelineBase
  * start, end offset is optional : introduce BitPosParams class
  * Unit test included