adding extra_args for command line

[minid33]

This is a simple and (maybe too) crude attempt to make arbitrary command line arguments.

Using an 'eval''d python dictionary we can pass key, values directly to the jinja template.

If you'd like this as it is feel free to accept the contribution :)

[kolypto]

@minid33 , sorry for the delayed response. I do really believe that feeding data like this is an antipattern: it just won't look pretty. But thanks for the idea, because...

here's the new feature: --import-env=name that will import all environment variables into the template under the name dict. Hope this helps!