drop Python 2.7 support

Python 2.7 EOL is arriving on 2020-01-01: https://pythonclock.org/

This will allow us to use Python 3 only libraries, like python-barcode,
which can maintain a reduced, simpler codebase, due to only one version
to support.

Closes #371.

Signed-off-by: Romain Porte <microjoe@microjoe.org>

examples/codepage_tables.py

@@ -1,7 +1,6 @@
 """Prints code page tables.
 """
 
-from __future__ import print_function
 
 import six
 import sys