Add OS auto-detect URL for binary downloads

[Vgr255]

I would like a link that will automatically detect the OS and architecture a user is running, and then give them the proper binary file, without any further input required from them.

Concrete use case: I have a program which is mostly aimed at Windows users, and I know that most of the people interested don't know much about computers, and "Click here then click on 'Download Python 3.5.2'" is sometimes too much to ask of them...

A few ideas: python.org/download/3 for latest 3.x, python.org/download/3.5 for latest 3.5, etc.
We could also have python.org/download/3 give whatever latest working release on the user's OS works (e.g. 3.4.4 on Windows XP, 3.5.x on everything else), but that's not why I'm opening this, anyway.

[berkerpeksag]

We already have a similar feature for the main "Downloads" menu but yes we need to make /downloads/* pages more user friendly.

[cefn]

If there's an initiative to make /downloads/* more user friendly, I have raised some additional concerns and made some additional suggestions in #1266