doc/json: make sure links are correctly passed to marked

Previously, an attempt was made to make sure the links state is
inherited. Unfortunately, this support was not complete, which
results in various unresolved links in the JSON output (as an
example, [1] contains `initialized by calling
[<code>buf.fill(fill, encoding)</code>][<code>buf.fill()</code>]`).

This commit completes that attempt. After this commit, individual
instances of the parser (for descriptions) inherit the links state
from the root lexer, so that individual Markdown links in descriptions
could be resolved. That same example is now substituted with
`initialized by calling <a href=\"#buffer_buf_fill_value_offset_end_encoding\"><code>buf.fill(fill, encoding)</code></a>`.

[1]: https://nodejs.org/api/buffer.json

PR-URL: https://github.com/nodejs/node/pull/8494
Reviewed-By: Roman Reiss <me@silverwind.io>

tools/doc/json.js

@@ -109,6 +109,7 @@ function doJSON(input, filename, cb) {
           current.shortDesc = current.desc;
           current.desc = [];
         }
+        current.desc.links = lexed.links;
         current.desc.push(tok);
         state = 'DESC';
       }
@@ -144,6 +145,7 @@ function doJSON(input, filename, cb) {
     }
 
     current.desc = current.desc || [];
+    current.desc.links = lexed.links;
     current.desc.push(tok);
 
   });