util.py: quote failed command for readability
Introduce 'retry' option

Add a 'retry' option which allows to configure how many
retries pip should make before giving up on HTTP request.

When the retries count is specified by user, its value is
passed to HTTPAdapter from requests which handles all
the underlying operations.
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
Special case os.devnull for PIP_CONFIG_FILE to mean 'no config file'
Merge pull request #1544 from pfmoore/devnull

Special case os.devnull for PIP_CONFIG_FILE to mean 'no config file'
'pip wheel' should download wheels, when it finds them

Conflicts:
	pip/commands/wheel.py
	pip/download.py
	pip/req/req_set.py
	pip/wheel.py
when file urls have hash fragments, check it
fixes for downloading wheels (Issue #1112)

Conflicts:
	pip/req/req_set.py
cherry-pick fixes
update changelog
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