Fix byte2int() for Python 3

Provides a fix for byte2int() using the Python 2 implemention on Python
3 when the "six" module isn't present

_lz4.py

@@ -12,8 +12,15 @@
     except ImportError:
         xrange = range
 
-        def byte2int(_bytes):
-            return ord(_bytes[0])
+        # If we're running Python 3 or newer, we must
+        #  define byte2int differently than with Python 2
+        import sys
+        if sys.version_info[0] >= 3:
+            import operator
+            byte2int = operator.itemgetter(0)
+        else:
+            def byte2int(_bytes):
+                return ord(_bytes[0])
 
     class CorruptError(Exception):
         pass