Host the Python docs on ReadTheDocs

From time to time the discussion arise about moving docs.python.org to readthedocs, there's even an experimental python.readthedocs.io.

I think there's many pros and cons of using readthedocs.

I'd personally be in favor of it if we (the PSF) support them (the cpython Doc is a big one with a lot of traffic, it take around 24h of CPU to build all versions × languages with all PDF A4, PDF letter, HTML, plaintext, epub).

In the other hand it's not an easy task, among other things docs.python.org is not only about generating the docs but also hosting history:

• https://docs.python.org/release/ (this is all the tagged commits in the cpython repo)
• https://docs.python.org/2.0/ (yes we keep old versions, and I'm not willing to see this disapear)

Inizia esaminando l’hosting e il processo di build attuali di docs.python.org, quindi confrontali con la configurazione sperimentale di python.readthedocs.io. Presta particolare attenzione alla cronologia delle release, a Python 2.0 e alle altre versioni meno recenti, nonché al carico di build indicato per più versioni, lingue e formati. Il lavoro sarà considerato completato quando sarà disponibile un piano di migrazione concreto che preservi tali requisiti e risolva i compromessi tra PSF e hosting.