Lex contents of <script> tags as plain text.

When lexing input in HTML mode the lexer has to treat _all_ content of a
<script> tag as plain text. This ensures that the lexer can process input such
as "x <y" and "// <foo>" correctly.

Fixes #70.

lib/oga/xml/lexer.rb

@@ -40,6 +40,14 @@ module Oga
     class Lexer
       attr_reader :html
 
+      ##
+      # Element name used to determine if a tag being processed is a Javascript
+      # tag.
+      #
+      # @return [String]
+      #
+      SCRIPT_TAG = 'script'.freeze
+
       ##
       # @param [String|IO] data The data to lex. This can either be a String or
       #  an IO instance.
@@ -181,6 +189,15 @@ module Oga
         return @elements.last
       end
 
+      ##
+      # Returns true if the current element is the HTML `<script>` element.
+      #
+      # @return [TrueClass|FalseClass]
+      #
+      def inside_html_script?
+        return html? && current_element == SCRIPT_TAG
+      end
+
       ##
       # Called when processing a single quote.
       #