Update README to talk about types instead of classes
Remove unused Rip::Core::System.class_property
Replace Rip::Core::Base.class_instance with Rip::Core::Base.type_instance

Also replace Rip::Core::Base.define_class_instance with Rip::Core::Base.define_type_instance
Replace internal :class with :type
Replace internal superclass(es) with super_type(s)
Replace internal klass with type (when referring to a Rip type)
Replace internal class_to_s with type_to_s
Replace Rip::{Core,Nodes}::Class with Rip::{Core,Nodes}::Type
Replace remaining internal references to class with type
Replace class keyword with type
Replace `class` keyword with `type` [TR #40]