Preregister refactor (#17)

* Build preregister on register; guard against undeducible class names

* Move preregister above since to give some nicer flow

* Remove preregister added on the Abstract provider

lib/oaken.rb

@@ -27,12 +27,6 @@ def initialize(type)
     def update(id, **attributes)
       self.class.define_method(id) { find(id) }
     end
-
-    def preregister(names)
-      names.each do |name|
-        register name
-      end
-    end
   end
 
   class Stored::Memory < Stored::Abstract
@@ -70,17 +64,16 @@ module Data
     extend self
 
     class Provider < Struct.new(:data, :provider)
-      def register(type, key = Oaken.inflector.tableize(type.name))
-        stored = provider.new(type)
-        data.define_method(key) { stored }
-      end
-
       def preregister(names)
         names.each do |name|
-          stored = provider.new(Oaken.inflector.classify(name).constantize)
-          data.define_method(name) { stored }
+          type = Oaken.inflector.classify(name).safe_constantize and register type, name
         end
       end
+
+      def register(type, key = Oaken.inflector.tableize(type.name))
+        stored = provider.new(type)
+        data.define_method(key) { stored }
+      end
     end
 
     def self.provider(name, provider)