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

See 90b87566 for context

- Note the following exception replacements:
  mwclient.errors.HTTPError -> requests.exceptions.ConnectionError
  mwclient.errors.HTTPStatusError -> requests.exceptions.HTTPError
  mwclient.errors.HTTPRedirectError -> requests.exceptions.TooManyRedirects

- Removed the `compability.old_upload` method, which was used for
  MediaWiki < 1.16.

- Requests automatically decompresses gzip-encoded responses, and
  does its best to decode response content to unicode when possible.

- [#53] Using the Responses library to mock http requests in tests

- 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)