Support for T-Digest data structure

[filipecosta90]

Given RedisBloom/RedisBloom#285 there is the following set of commands we should enable:

• TDIGEST.CREATE: Allocate a new histogram
• TDIGEST.RESET: Empty out a histogram and re-initialize it
• TDIGEST.ADD: Add a value to the t-Digest with the specified count
• TDIGEST.MERGE: Merge one t-Digest into another
• TDIGEST.CDF: Returns the fraction of all points added which are ≤ x.
• TDIGEST.QUANTILE: Returns an estimate of the cutoff such that a specified fraction of the data added to the t-Digest would be less than or equal to the cutoff.
• TDIGEST.MIN: Get the minimum value from the histogram. Will return DBL_MAX if the histogram is empty
• TDIGEST.MAX: Get the maximum value from the histogram. Will return DBL_MIN if the histogram is empty
• TDIGEST.INFO : Returns compression, capacity, total merged and unmerged nodes, the total compressions
  made up to date on that key, and merged and unmerged weight.

With the in-depth params in https://oss.redislabs.com/redisbloom/master/TDigest_Commands/