Add documents on auto-merge

Remove restriction for jaraco - only members with access can create labels, so it's secure enough to restrict based on the label.

Only allow auto-merge PRs submitted by authorized users

Add declaration indicating the PEP 517 build backend needed for building setuptools.

Import distribution in doctest

This both prevents the warning from surfacing during the tests and
ensures that no regressions occur.

Fixes GH issue #1612, bug introduced in commit 0902f02d

Remove use of splituser

added unittest for _download_git

Backend should not say that setuptools is needed to build

Fix issue with missing author metadata

Prior to this patch, if the author or author_email were omitted from
`setup`, a malformed `PKG-INFO` would be created.

Fix Travis test for pyc files in egg-info

`!` is a special character in YAML syntax, so this was being interpreted
as `grep pyc ...`, not `! grep pyc ...`

I've also added the same `pyc` test to the normal tests.

Release 40.6.0