ZstdDecompressor stream_reader doesn't support readline()

[gcp]

The documentation for ZstdCompressor explicitly says that stream_reader's file-like object doesn't support readline() because it makes no sense for compressed data. For Decompressor, this remark is missing - as it should be - but the function doesn't seem to be implemented and throws NotImplementedError.

[gcp]

python-zstandard/c-ext/decompressionreader.c

Line 263 in b3b44ff

PyErr_SetNone(PyExc_NotImplementedError);

[indygreg]

I'm going to call this a duplicate of #13.

I have a patch for readline() that's been sitting around. I need to polish it up and land it. I'm not a fan of adding a buffering layer in order to provide readline(). But enough consumers want a file-like object and readline() is part of that interface. So it should be implemented. I'll try to deliver this in the 0.9 release.