The open API is inconsistent

Iterating over text data works as expected:

In [2]: for line in zstandard.open('123.zst', 'rt'):
   ...:     print(line)
   ...:
123

Iterating over binary data raises an exception:

In [4]: for line in zstandard.open('123.zst', 'rb'):
   ...:     print(line)
   ...:
---------------------------------------------------------------------------
UnsupportedOperation                      Traceback (most recent call last)
<ipython-input-4-42009a852259> in <module>
----> 1 for line in zstandard.open('123.zst', 'rb'):
      2     print(line)

UnsupportedOperation:

I think it makes sense to wrap binary reader/writer in io.BufferedReader/io.BufferedWriter.
Most libraries provide the same interface for text and binary streams.

Start at the zstandard.open entry point and compare how its text and binary readers handle iteration. Check the binary reader and writer behavior against io.BufferedReader and io.BufferedWriter; done means binary streams support iteration without UnsupportedOperation while preserving the existing text behavior.