Add info to Code

Closes GH-22.

Reviewed-by: Christian Murphy <Christian.Murphy.42@gmail.com>
Reviewed-by: Titus Wormer <tituswormer@gmail.com>

readme.md

@@ -157,14 +157,17 @@ Yields:
 ### `Code`
 
 `Code` ([`Text`][text]) occurs at block level (see
-[`InlineCode`][inlinecode] for code spans).  `Code` sports a language
-tag (when using GitHub Flavoured Markdown fences with a flag, `null`
-otherwise).
+[`InlineCode`][inlinecode] for code spans).  `Code` supports an
+info string and a language tag (when the line with the opening fence
+contains some text, it is stored as the info string, the first word
+following the fence is stored as the language tag, the rest of the
+line is stored as the info string, both are null if missing)
 
 ```idl
 interface Code <: Text {
   type: "code";
   lang: string | null;
+  info: string | null;
 }
 ```
 
@@ -180,6 +183,7 @@ Yields:
 {
   "type": "code",
   "lang": null,
+  "info": null,
   "value": "foo()"
 }
 ```