Add dependency for pathlib on Python 2.7 (for tifffile)

[pmiddend]

I'm trying to build imageio with Python 2.7, but this fails because you're using pathlib:

/nix/store/msknadbwcwvm7n9lynl95yv4ialawf8g-python2.7-imageio-2.5.0/lib/python2.7/site-packages/imageio/core/functions.py:259: in imwrite
    writer = get_writer(uri, format, "i", **kwargs)
/nix/store/msknadbwcwvm7n9lynl95yv4ialawf8g-python2.7-imageio-2.5.0/lib/python2.7/site-packages/imageio/core/functions.py:187: in get_writer
    return format.get_writer(request)
/nix/store/msknadbwcwvm7n9lynl95yv4ialawf8g-python2.7-imageio-2.5.0/lib/python2.7/site-packages/imageio/core/format.py:178: in get_writer
    return self.Writer(self, request)
/nix/store/msknadbwcwvm7n9lynl95yv4ialawf8g-python2.7-imageio-2.5.0/lib/python2.7/site-packages/imageio/core/format.py:214: in __init__
    self._open(**self.request.kwargs.copy())
/nix/store/msknadbwcwvm7n9lynl95yv4ialawf8g-python2.7-imageio-2.5.0/lib/python2.7/site-packages/imageio/plugins/tifffile.py:285: in _open
    load_lib()
/nix/store/msknadbwcwvm7n9lynl95yv4ialawf8g-python2.7-imageio-2.5.0/lib/python2.7/site-packages/imageio/plugins/tifffile.py:36: in load_lib
    from . import _tifffile
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

    """

    from __future__ import division, print_function

    import sys
    import os
    import io
    import re
    import glob
    import math
    import zlib
    import time
    import json
    import enum
    import struct
>   import pathlib
E   ImportError: No module named pathlib

[almarklein]

I think we missed that the tifffile module (that we copy along) now depends on pathlib, so we have not put pathlib in our dependencies for 2.7.

For now, you can just pip install pathlib and it should work.

[dotlambda]

@almarklein If I understand it correctly, pathlib will be an optional dependency on Python 2.7 in the future?

[almarklein]

No, it's a hard dependency (for Python 2.7). In the future, new versions of imageio will no longer support Python 2.7.

[almarklein]

Closing since Python 2.7 is no longer supported.