Handle parsing of HTML <style> tags.

This basically re-applies the technique used for HTML <script> tags. With this
extra addition I decided to rename/normalize a few things so it's easier to add
any extra tags in the future. One downside of this setup is that the following
will not be parsed by Oga:

    <style>
        </script>
    </style>

The same applies to script tags containing a literal </style> tag. Since this
particular case is rather unlikely to occur I'm OK with not supporting it as it
_does_ simplify the lexer quite a bit.

Fixes #80

ext/java/org/liboga/xml/Lexer.rl

@@ -187,14 +187,13 @@ public class Lexer extends RubyObject
     }
 
     /**
-     * Returns true if we're in an HTML script tag. See
-     * Oga::XML::Lexer#inside_html_script? for more information.
+     * See * Oga::XML::Lexer#literal_html_element? for more information.
      */
-    public Boolean inside_html_script_p()
+    public Boolean literal_html_element_p()
     {
         ThreadContext context = this.runtime.getCurrentContext();
 
-        return this.callMethod(context, "inside_html_script?").isTrue();
+        return this.callMethod(context, "literal_html_element?").isTrue();
     }
 }