New draft code of conduct

Myself and others have been working towards the Matplotlib project adopting its own Code of Conduct. Previously Matplotlib deferred to the Python code of conduct. We would like to explicitly adopting the same text, with some minor changes to make it specific to the Matplotlib community.

We would like to solicit feedback on the draft code of conduct, which can be found in this pull request: If you have any comments, please add them to the pull request.

The pull request will be open for comments for the next two weeks, and unless there are significant issues or disagreements brought up, we will start moving to adopt it on the 13th October.