Pass string instead of Path object to open

[hankso]

What is the error

A path object cannot be directly opened like a filename string.

How to reproduce

>>> from pathlib import Path
>>> p = Path('xdf_sample.xdf')    # it's a path object
>>> open(Path('xdf_sample.xdf'))  # but open only accept str / bytes
TypeError: invalid file: PosixPath('xdf_sample.xdf')

Same as gzip.open

>>> import gzip
>>> gzip.open(Path('foo'))
TypeError: filename must be a str or bytes object, or a file

How to fix

>>> p = Path('foo')
>>> open(str(p))

---

BTW, I suggest NOT to mix using os.path and pathlib. So all os.path functions are replaced.

Please consider merging.

Python 3.5.2
Ubuntu 16.04

[cboulay]

This is a 3.5 backwards compatibility patch. In Python 3.6 and up, open accepts Pathlike objects.
It looks good to me. Thanks for the PR!

[cbrnr]

@hankso would you like your real name to be shown in the changelog for your contribution?