Merge branch 'master' into 3.7 (Please see detailed commit message)

This is a rather complicated way to copy README and TRANSLATORS files on
master to 3.7, for the sake of keeping the commit history.

Notes:
1. The commit history has been refined, previously there are useless
   commits such as "Fix formatting", these commits have been squashed.
2. The merge commit only keeps README.rst and TRANSLATORS, the
   additional sphinx.po originally on master has been removed in this
   merge commit since there's also a sphinx.po in 3.7 branch.
3. These adjustments are done locally, so the master branch on remote
   should stay the same as it originally was.

Author: adrianliaw