Use io.open() instead of open() for consistency

Recommended in the Python docs (https://docs.python.org/3/howto/pyporting.html#text-versus-binary-data):
"(...) You should also use io.open() for opening files instead of
the built-in open() function as the io module is consistent
from Python 2 to 3 while the built-in open() function is not
(in Python 3 it’s actually io.open())."

Author: generalmimon

kaitaistruct.py

@@ -1,7 +1,7 @@
 import itertools
 import sys
 import struct
-from io import BytesIO, SEEK_CUR, SEEK_END  # noqa
+from io import open, BytesIO, SEEK_CUR, SEEK_END  # noqa
 
 PY2 = sys.version_info[0] == 2