Add a __dir__ attribute to a closed namespace

[tonyfast]

Proposed Changes

• This change is introduced for improved affordance when working with rdflib in interactive settings like IPython.
• The dir attribute gives attribute completion.
• Use the mangled attribute from the closed namespace object to give better interactive completion.

Closes #918

[coveralls]

Coverage increased (+0.1%) to 75.789% when pulling a5ccaee on tonyfast:patch-1 into e4fe0fd on RDFLib:master.

[nicholascar]

Hi @tonyfast, thanks for this PR. I don;t know much about iPython myself but fully support people using it.

Can you please just put a comment in about how this approach is better than this approach: PR #918? Code is very similar. If we merge your code, we will close #918 (or vice versa!).

[tonyfast]

Oh wow. yea that pr is basically the same thing. In #918, I personally can't get at the __uris property the author is using there. Since the getattr and getitem work the same on the closed namespace the key completions (which returns getitem completion) should be equivalent to the getattr/__dir__ completion.

I made this PR on 5.0 so maybe it is up to date with the api.

[nicholascar]

@tonyfast we'll merge this one in and close the older #918. We'll leave it to Jupyter users to flag any issues (I've only just started making RDFlib Jupyter training material myself!).