Add remote repos in python command line arguments

[operatorequals]

Starting a Python process with preinstalled remote repos would be useful. Something like the following:

$ python -m httpimport --insecure github://operatorequals/covertutils http://somerepo:8000/python-packages
[...]
>>> import covertutils
>>>

For this issue to be implemented, Issue 21 has to be implemented first, to not declare what packages should be implemented from given URLs.