allow to patch class-attributes with builtin types

today i stumbled upon a similar problem a @davidjb suggested to fix in PR #2 too.

now you can do this too:

configure.zcml:
```
  <include package="collective.monkeypatcher" />
  <monkey:patch
    description="support pfg embedded forms https://github.com/smcmahon/Products.PloneFormGen/issues/130"
    class="plone.app.viewletmanager.manager.BaseOrderedViewletManager"
    original="_uncatched_errors"
    replacement=.patched_uncatched_errors"
    />
```

___init__.py:
```
patched_uncatched_errors = (ConflictError, KeyboardInterrupt, Retry)
```

in addition i did some flake8 cleanup and moved docs/HISTORY.txt to /CHANGES.rst to follow best practice