Allow arbitrary bytes in output. Resolves #245

testing/resources/arbitrary_bytes_repo/python3_hook/main.py

@@ -0,0 +1,13 @@
+# -*- coding: utf-8 -*-
+from __future__ import print_function
+from __future__ import unicode_literals
+
+import sys
+
+
+def func():
+    # Intentionally write mixed encoding to the output.  This should not crash
+    # pre-commit and should write bytes to the output.
+    sys.stdout.buffer.write('☃'.encode('UTF-8') + '²'.encode('latin1') + b'\n')
+    # Return 1 to trigger printing
+    return 1