1-D array of data being analyzed
          m: embedding dimension (order of permutation entropy) 
          tau: time delay
outputs - permuEnt: value calculated using a log base of 2
          hist: number of occurences for each permutation order
Remarks
- It differs from the permutation entropy code found on MatLab Central in
  one way (see MathWorks reference). The code on MatLab Central uses the 
  log function (base e, natural log), whereas this code uses log2 (base 2
  ), as per Bandt &amp; Pompe, 2002