Added license text and import from future.

This code did not work for Python 2.x becaus I was not
importing from future. While I was altering all the files
I updated the header to include license information.

code/pf_internal.py

@@ -1,3 +1,22 @@
+# -*- coding: utf-8 -*-
+
+"""Copyright 2015 Roger R Labbe Jr.
+
+
+Code supporting the book
+
+Kalman and Bayesian Filters in Python
+https://github.com/rlabbe/Kalman-and-Bayesian-Filters-in-Python
+
+
+This is licensed under an MIT license. See the readme.MD file
+for more information.
+"""
+
+from __future__ import (absolute_import, division, print_function,
+                        unicode_literals)
+
+
 from filterpy.monte_carlo import stratified_resample
 import matplotlib as mpl
 import matplotlib.pyplot as plt
@@ -5,7 +24,6 @@ import matplotlib.pyplot as plt
 import numpy as np
 from numpy.random import randn, random, uniform, multivariate_normal, seed
 #from nonlinear_plots import plot_monte_carlo_mean
-import pylab as plt
 import scipy.stats
 from RobotLocalizationParticleFilter import *