* Continuation of updating code to Python 3 with Python 2 fallback.
* Using io.open allows files to be encoded and decoded automatically on write and read. This
maintains the python boundaries of unicode in code and bytes for output/files so less
explicit encoding or decoding.
* io.StringIO is the replacement for StringIO and will only accept unicode strings.
* io.BytesIO is used where bytes output is required by the enclosing method.
* Update bencode for full compatibility.
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