Fixes #117 `utilities.py:_open_for_write` no longer has a race condition

[rawrgulmuffins]

Fixes #117

Changes

• Modified _open_for_write now uses a try, except for file existence checking instead of using a if os.exists check.

NOTE

Normally I'd write a unit test for this kind of change. If we were using threads I would write the test by injecting a conditional lock into the main thread after the if os.exists check.

I don't know how to do that with multiprocess. If you know how that can be accomplished I'd love to include that test.

[rawrgulmuffins]

Switching over to Pathlib2 solution for this issue.