external merge sort

simulates external merge sort.

This program simulates the problem of sorting the pages of a file on a
disk.Suppose we have 100,000 pages in a file in a database then if we have to sort records of this file,then we can do it with 3 buffer pages
only and that too in only 17 passes.This program will create sorted intermediate runs(files) and finally a single run(file) with all the records in all the pages n the disk sorted.