Update Code of Conduct.

@NodeDC/organizers @Bantik @sigmavirus24 /cc @jonathana @sandinmyjoints

Based on feedback from #1 which, in turn, is based on:
- http://speakup.io/coc.html
- https://www.djangoproject.com/conduct/
- http://geekfeminism.wikia.com/wiki/Conference_anti-harassment/Policy

Aims to replace #1.