Allows for ASDF system to be connected so that auto-loading may occur

 ASDF-System-Connections provides auto-loading of systems that only make
 sense when several other systems are loaded. If I'm lucky, an example will
 make this clear! CL-Containers and CL-Variates are separate systems and can
 therefore be loaded independently. If both of them are loaded, however,
 then it makes sense to also load code that uses CL-Variates to sample
 random elements from containers. Rather than requiring you to remember to
 load that extra system (and to load it only after both Cl-Containers and
 CL-Variates are loaded), ASDF-System-Connections lets you set things up so
 that loading happens automatically.