Simplify __main__ logic

runner.py seemed to exist for the sole function of containing
a simple function that was called by __main__.py.

I've simply removed that file with its function moved into
__main__.py itself; no functionality should be expected to change.
Make main even simpler
Revert "Use Travis to handle the Matrix"

This reverts commit 01894aee7be04fb0756f4e73a462ccf5ae2c886f.
Cleanup after each test case
Merge pull request #1550 from dstufft/revert-dynamic-toxenv

Revert "Use Travis to handle the Matrix"
Make main as simple as possible!
rabble rabble rabble
Merge pull request #1546 from dstufft/cleanup-temp

Cleanup after each test case
Merge pull request #1536 from Ivoz/cleanup_main

Simplify __main__ logic
pip docs refactor
Merge pull request #1556 from pypa/docs_refactor

pip docs refactor
dropped support for Python 3.1
Documentation for --exists-action option

Fixes #1458
Merge pull request #1568 from coagulant/feature/document-exists-action

Documentation for --exists-action option
This is no longer in use
Merge pull request #1575 from dstufft/remove-unused-constant

Remove an unused constant