Rank operator is at PIG! :’)

Ok, maybe it happened some time ago (one month?). But, I was bussy!
Some good news after 2 months and a half of hard work, guided by Gianmarco De Francisci Morales, I don’t have words to thank him for his time and advices along this process.
Now, it’s time for formal documentation (working on, hopefully this week I’ll finish it! hurra!) and use it!
My pleasure:  https://issues.apache.org/jira/browse/PIG-2353