Allow comparison with enum classes

This addresses the issue of using enums in a case statement and also
makes the API more predictable.

lib/classy_enum/collection.rb

@@ -21,6 +21,8 @@ module Collection
     def <=> other
       if other.is_a?(Symbol) || other.is_a?(String)
         other = self.class.find(other)
+      elsif other.is_a?(Class)
+        other = other.new
       end
 
       index <=> other.index

spec/classy_enum/collection_spec.rb

@@ -35,6 +35,7 @@ class ClassyEnumCollection::Three < ClassyEnumCollection
 
   context '#<=> (equality)' do
     its(:first) { should == ClassyEnumCollection::One.new }
+    its(:first) { should == ClassyEnumCollection::One }
     its(:first) { should == :one }
     its(:first) { should == 'one' }
     its(:first) { should_not == :two }