15 puzzle solver

15 puzzle solver is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Your task is to write a programm that solves the Fifteen Puzzle Game in the fewest number of moves.
For this task you will be using the following puzzle:

15 14  1  6
 9 11  4 12
 0 10  7  3
13  8  5  2

Solution:

 1  2  3  4
 5  6  7  8
 9 10 11 12
13 14 15  0

The output must show the moves' directions, like so: left, left, left, down, right... and so on.