Make TDMS file paths use pathlib.Path

[epage]

Good

• pathlib is nice to work with

Bad

• Didn't exist or was provisional until Python 3.6
  • The pypi version might be compatible enough as a backport?

[bkeryan]

I think the minimum fix is to update these API methods to accept either a str or a pathlib.PurePath:

• InStream.logging_file_path setter
• InStream.start_new_file()
• PhysicalChannel.configure_teds()

I think this would be a nice-to-have, but it would break compatibility. If we don't do it in 1.0, we might not get another chance:

• InStream.logging_file_path getter returns pathlib.Path