Improved portability between Python 2 and Python 3. Beginnings of code for writing SEG Y.

util.py

@@ -2,6 +2,8 @@ import itertools
 import time
 import os
 
+from portability import izip
+
 
 def pairwise(iterable):
     """Pairwise iteration.
@@ -14,7 +16,7 @@ def pairwise(iterable):
     """
     a, b = itertools.tee(iterable)
     next(b, None)
-    return itertools.izip(a, b)
+    return izip(a, b)
 
 
 def contains_duplicates(sorted_iterable):