"require EXPR" only accepts "Class/Name.pm" style module names, not
"Class::Name". How frustrating! For that, we provide "load_class
'Class::Name'".
It's often useful to test whether a module can be loaded, instead of
throwing an error when it's not available. For that, we provide
"try_load_class 'Class::Name'".
Finally, sometimes we need to know whether a particular class has been
loaded. Asking %INC is an option, but that will miss inner packages and
any class for which the filename does not correspond to the package
name. For that, we provide "is_class_loaded 'Class::Name'".
