pipreqs circumvents pip.ini; feature request: use pip.ini if it exists.

[ebmoll]

I'm behind a corporate proxy and use pip.ini to set the proxy. If i run pipreqs without the --proxy ... argument, it doesn't find the pypi repos. It would be very cool if pipreqs could use the proxy settings from pip.ini.

[hliebert]

I am also facing this problem, using the settings from pip.ini would be great.