Python 3 support (#755)

* Python 3 support

* Fix import_vs_environment in xenia-build

* Drop support for Python 2

* Fix CIs and xb.bat

* Require Python3.4+ because of Ubuntu Trusty

* popen.communicate returns bytes instead of string

* Useful info in travis

* universal_newlines should be True

* Changed shebang to python 3

* Python 3 shebang fix

* Clang python 3 shebang fix

tools/diff.py

@@ -1,3 +1,7 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+"""python diff.py file1 file2 diff"""
+
 import difflib
 import sys
 
@@ -5,4 +9,4 @@ diff = difflib.unified_diff(
     open(sys.argv[1]).readlines(),
     open(sys.argv[2]).readlines())
 with open(sys.argv[3], 'w') as f:
-  f.write(''.join(diff))
+    f.write(''.join(diff))