This commit updates some outdated syntax with the modern alternatives.
The changes were applied automatically using pyupgrade (v2.0.1) with the
following command:

```
pyupgrade --py3-plus **/*.py
```

These updates are purely syntactical and there should be no change in
functionality.

writeapi is being removed

Bug: T294397

Closes #207

Examples should adhere to PEP-8 guidelines, as these examples
not only document how to use correctly the client, but also
will serve as a first exposition to Python for some contributors.

Reference: https://www.python.org/dev/peps/pep-0008/

* make basic_edit.py and upload.py python-3 compatible

- Keep automated tests to be run with py.test in './tests/'
  and examples in './examples/'
- Rename test to adhere to 'Conventions for Python test discovery'
  (http://pytest.org/latest/goodpractises.html#test-discovery)