Use attr_reader for a couple methods

attr_reader methods are faster than normal methods.

lib/tilt.rb

@@ -8,9 +8,9 @@ module Tilt
 
   @default_mapping = Mapping.new
 
-  # @return [Tilt::Mapping] the main mapping object
-  def self.default_mapping
-    @default_mapping
+  class << self
+    # @return [Tilt::Mapping] the main mapping object
+    attr_reader :default_mapping
   end
 
   # @private

lib/tilt/template.rb

@@ -155,9 +155,7 @@ module Tilt
     # default_encoding-option if present. You may override this method
     # in your template class if you have a better hint of the data's
     # encoding.
-    def default_encoding
-      @default_encoding
-    end
+    attr_reader :default_encoding
 
     # Do whatever preparation is necessary to setup the underlying template
     # engine. Called immediately after template data is loaded. Instance