pigar -c doesn't handle referenced files or other flags well

[Gerrit-K]

Not a big deal, but pigar treats arguments in requirements.txt files as packages. E.g. sometimes you want to split your requirements or allow private package repositories:

requirements.txt:

pigar == 0.9.0
-r pigar-requirements.txt

--extra-index-url ...
--trusted-host ...
-r private-requirements.txt

Pigar will not treat them differently, but search on pypi.org

[bganglia]

@damnever I can work on adding split requirements files, but that will still leave private package repositories.

[damnever]

@bganglia PRs are appreciated!