Make sure pretty_hex works under Python 2 and Python 3.

 * Run doctests under tox.
 * Add pretty_hdex doc tests for string, bytes and unicode

Fixes tinyfpga#48

Author: mithro

programmer/check_doctests.py

@@ -0,0 +1,4 @@
+#!/usr/bin/env python
+import doctest
+import tinyprog
+doctest.testmod(tinyprog)