[3.3] Backport CI config from master by vstinner · Pull Request #2481 · python/cpython

Add .travis.yml for Travis CI.

The regen-all Makefile rule doesn't exist in Python 3.4, only since
Python 3.5 and newer (and 2.7).

tzdata resource doesn't exist in Python 3.4.

Fixing Sphinx warnings requires to backport huge intrusive changes
like:

- commit d97b7dc
- commit 5c67933

The public cyrus.andrew.cmu.edu IMAP server (port 993) doesn't accept
TLS connection using our self-signed x509 certificate. Remove the two
tests which are already skipped.
(cherry picked from commit 7895a05)