Update CONDUCT.md

Some very quick changes to the CoC. Namely:
- More consistent language. Extend the first person to all paragraphs, and treat the ones following the first as an implicit extension of the pledge.
- A few more considerations on communication and tolerance. The statement on diversity is taken from the [Python Community](http://www.python.org/community/diversity/). For future reference, their [Code of Conduct](http://www.python.org/psf/codeofconduct/) is also very good.