Move PathManager methods into its singleton class

lib/jekyll/path_manager.rb

@@ -16,11 +16,12 @@ module Jekyll
     # This class cannot be initialized from outside
     private_class_method :new
 
+    class << self
       # Wraps `File.join` to cache the frozen result.
       # Reassigns `nil`, empty strings and empty arrays to a frozen empty string beforehand.
       #
       # Returns a frozen string.
-    def self.join(base, item)
+      def join(base, item)
         base = "" if base.nil? || base.empty?
         item = "" if item.nil? || item.empty?
         @join ||= {}
@@ -32,7 +33,7 @@ module Jekyll
       # and prepends the questionable path with the base directory if false.
       #
       # Returns a frozen string.
-    def self.sanitized_path(base_directory, questionable_path)
+      def sanitized_path(base_directory, questionable_path)
         @sanitized_path ||= {}
         @sanitized_path[base_directory] ||= {}
         @sanitized_path[base_directory][questionable_path] ||= begin
@@ -60,3 +61,4 @@ module Jekyll
       end
     end
   end
+end