Create association_rule.java

All code is not mine. I combined different codes.
You can see the original of the codes and modify a bit
to fit your problem.
source 1. http://rosettacode.org/wiki/Power_Set#Java --> power set generetaor
source 2. http://chimpler.wordpress.com/2013/05/02/finding-association-rules-with-mahout-frequent-pattern-mining/ --> association rule- the basic structure is taken from this page.
source 3. http://sujitpal.blogspot.de/2013/09/search-rules-using-mahouts-association.html --> iteratively reading from each file generated by hadoop.

Why I need to modify the java code if they are already available
1. the codes only generate association rule with one antecedent and consequent.
2. the second link only shows how to generate association rule from a single file but the third source solves this problem but it is written in scala, I was working with java.