Attempt to look up non-existing settings in parent classes (see sover…

…an#21)

This fixes an issue where settings added to Cuba.settings *after* inheriting from
`Cuba` are not picked up by the child classes. The issue is described in issue

Settings are lookup up in the settings Hash of the parent class if a setting does
not exist using `Hash#default_proc`. The settings Hash is still deepcloned, so
they're still overridable.

lib/cuba.rb

@@ -86,11 +86,26 @@ def self.settings
   end
 
   def self.deepclone(obj)
-    Marshal.load(Marshal.dump(obj))
+    # Hashes with a default_proc cannot be serialized by Marshal.dump.
+    if obj.respond_to?(:default_proc)
+      proc = obj.default_proc
+      obj.default_proc = nil
+    end
+
+    new_obj = Marshal.load(Marshal.dump(obj))
+
+    if obj.respond_to?(:default_proc)
+      obj.default_proc = proc
+    end
+
+    new_obj
   end
 
   def self.inherited(child)
     child.settings.replace(deepclone(settings))
+    child.settings.default_proc = proc do |hash,key|
+      hash[key] = self.settings[key]
+    end
   end
 
   attr :env

test/settings.rb

@@ -18,6 +18,22 @@ class Admin < Cuba; end
   assert_equal "baz", Admin.settings[:foo]
 end
 
+test "attempts to get absent settings from parent class" do
+  class User < Cuba; end
+  class PowerUser < User; end
+
+  Cuba.settings[:get_from_parent] = "x"
+
+  assert_equal nil, Cuba.settings[:does_not_exist]
+  assert_equal nil, User.settings[:absent]
+  assert_equal "x", User.settings[:get_from_parent]
+  assert_equal "x", PowerUser.settings[:get_from_parent]
+
+  Cuba.settings[:after_deepcloning] = "x"
+
+  assert_equal "x", User.settings[:after_deepcloning]
+end
+
 test do
   Cuba.settings[:hello] = "Hello World"