create offline mode for py2pack

[coogor]

if a package is already available, there is no point in contacting pypi again. So a kind of offline mode is desirable (it would work around issue #133 as well)

[toabctl]

py2pack takes iirc some infos from pypi, even if a package is available...

[mcepl]

@coogor What do you mean by “package already available”? Tarball is in the current directory? That isn’t enough, @toabctl is right, metadata are downloaded from PyPI not from a tarball.

[coogor]

Aha....was not aware of that. Yes, I meant that the package is available in the current directory