Update documentation, add a new key *skip_if_no_internet* to support
systems that **recommend** having an internet connection (but don't
require it), and which also use the packages module. This prevents
a long delay while the package manager tries to access the internet
and times out (repeatedly).
Existing configurations are unchanged.
- Check for 'list' when it's actually a 'dict' is strange.
Reverse logic to consider 'str' a package name and everything
else is special.
- Refactor to handle the difference between package names and
packages-with-script-data in one place.
- Add code and config documentation.
- Switch sample configurations to dummy-backend.
