Added Ace::LazyRendering mixin for lazy rendering.

* Just include it and redefine #source_files method.

lib/ace.rb

@@ -144,29 +144,13 @@ module Ace
       end
     end
 
-    def compare_mtime(one, others)
-      File.exist?(one) && File.mtime(one) > others.map { |post| File.mtime(post) }.max
-    end
-
-    def source_files
-      [self.original_path]
-    end
-
-    def fresh?
-      @fresh ||= compare_mtime(self.output_path, self.source_files)
-    end
-
     def save!
-      if self.fresh?
-        puts "~ [IGNORE] #{self.output_path}"
-      else
-        puts "~ [UPDATE] #{self.output_path}"
-        content = self.render # so filters can influence output_path
+      content = self.render # so filters can influence output_path
+      puts "~ [RENDER] #{self.output_path}"
 
-        FileUtils.mkdir_p File.dirname(self.output_path)
-        File.open(self.output_path, "w") do |file|
-          file.puts(content)
-        end
+      FileUtils.mkdir_p File.dirname(self.output_path)
+      File.open(self.output_path, "w") do |file|
+        file.puts(content)
       end
     end
   end

lib/ace/mixins/lazy.rb

@@ -0,0 +1,31 @@
+# encoding: utf-8
+
+# Sometimes rendering is taking too long, so you want to skip
+# it in case that nothing changed in the files which influence
+# the output. For example syntax highlighting via Pygments takes
+# a while, so it's better to include this mixin and redefine
+# #source_files to include every file which influence the output.
+module Ace
+  module LazyRendering
+    def compare_mtime(one, others)
+      File.exist?(one) && File.mtime(one) > others.map { |post| File.mtime(post) }.max
+    end
+
+    # @api public
+    def source_files
+      [self.original_path]
+    end
+
+    def fresh?
+      @fresh ||= compare_mtime(self.output_path, self.source_files)
+    end
+
+    def save!
+      if self.fresh?
+        puts "~ [IGNORE] #{self.output_path}"
+      else
+        super
+      end
+    end
+  end
+end