[Haml] Convert Haml::Error docs to YARD.

lib/haml/error.rb

@@ -1,22 +1,22 @@
 module Haml
   # An exception raised by Haml code.
   class Error < StandardError
-    # :stopdoc:
-
-    # By default, an error is taken to refer to the line of the template
-    # that was being processed when the exception was raised.
-    # However, if line is non-nil, it + 1 is used instead.
+    # The line of the template on which the error occurred.
+    #
+    # @return [Fixnum]
     attr_reader :line
 
+    # @param message [String] The error message
+    # @param line [Fixnum] See \{#line}
     def initialize(message = nil, line = nil)
       super(message)
       @line = line
     end
-    # :startdoc:
   end
 
   # SyntaxError is the type of exception raised when Haml encounters an
   # ill-formatted document.
-  # It's not particularly interesting, except in that it includes Haml::Error.
+  # It's not particularly interesting,
+  # except in that it's a subclass of {Haml::Error}.
   class SyntaxError < Haml::Error; end
 end