proposal: use magic marks in comments to help make better decisions

[damnever]

Just some random thoughts, something like this:

import a # pigar: requirements="package-a"

soup = BeautifulSoup(html, 'lxml') # pigar: requirements="lxml"

 # pigar: requirements="foo","bar == 1.0"
EXTRA_PACKAGES = ["foo", "bar"]

Maybe this is too much since pigar is not a package management tool, ref: https://github.com/damnever/pigar#faq

[damnever]

I think a command line option or a separate configuration file is acceptable.

[damnever]

Related issue: #32, #103