Redirect to equivalents of Python2 modules

[przemub]

For example it should redirect from https://docs.python.org/2/library/stringio.html to https://docs.python.org/3/library/io.html#io.StringIO (or at least include such an option/suggestion to the user).

Great extension by the way :)

[m4tx]

I believe that #4 fixes that — if not, please reopen the issue :)