(Splitting this out from #159)

#159 fixed the Downloads menu to include "Other Platforms" and "Alternative Implementations" links.

However, there's still a couple of gaps, which relates to the fact that:

1. On most *nix systems, one of your better options for obtaining CPython is usually the provider of the underlying OS
2. There are other pre-built options which also provide integrated update management, both commercially backed (e.g. ActivePython, EPD/Canopy, Anaconda), and community backed (homebrew, pyenv, pythonz)

To avoid overwhelming the main menu, I'm thinking a reasonable approach would be:

1. Add a single new "Redistributors" entry to the Downloads menu
2. Have the following subsections on that page:

• Linux, noting the availability of system packages, and linking to https://en.wikipedia.org/wiki/Linux_distribution#Widely_used_distributions
• BSD, noting the availability of system packages, and linking to https://en.wikipedia.org/wiki/List_of_BSD_operating_systems
• Other Community Redistributors, listing homebrew (Mac OS X only), pyenv (*nix), pythonz (cross-platform)
• Commercial Redistributors, listing (Copper-or-higher?) PSF Sponsors that offer commercial distributions of Python for on-premise use (Anaconda, ActiveState, Enthought, Red Hat, Intel)
• Cloud Providers, listing (Copper-or-higher?) PSF Sponsors that offer Python environments as part of a cloud service (Google, Microsoft, Rackspace, Red Hat)

The last two sections would be deliberately intended to offer a direct incentive for commercial redistributors and service providers to formally sponsor the PSF, above and beyond being included in the main PSF Sponsor list (the "Copper-or-higher" suggestion is there because $10/week seems low for such a commercial listing, while $40/week seems more reasonable)