[Sass] Convert Sass::Script::Bool docs to YARD.

lib/sass/script/bool.rb

@@ -1,13 +1,17 @@
 require 'sass/script/literal'
 
 module Sass::Script
-  class Bool < Literal # :nodoc:
+  # A SassScript object representing a boolean (true or false) value.
+  class Bool < Literal
+    # The Ruby value of the boolean.
+    #
+    # @return [Boolean]
+    attr_reader :value
+    alias_method :to_bool, :value
+
+    # @return [String] "true" or "false"
     def to_s
       @value.to_s
     end
-
-    def to_bool
-      @value
-    end
   end
 end