sys.link_group() starts a new 4C group or links to
an existing one.
A 4C group is a set of programs, pushed and linked, working together
as a group.
4C allows you to run multiple independant groups.
Each group maintains its own context and the user can switch
between groups with function keys.
The programmer can also switch between groups using sys.link_group().
The group name can be any alpha value.
The group name uniquely identifies a group.
Bugs/Features/Comments:
This group stuff is only experimental right now
and it will be better defined in the future.