Markdown link by id: allow code as id

Example markdown:

text [`code_link`][] text

[`code_link`]: http://example.com

Expected rendering:

text code_link text

Actual rendering:

text [code_link][] text

It annoying to walkaround by another id:

text [`code_link`][code_link] text

[code_link]: http://example.com

The shortcut [`code_link`][] will help to write a documentations with markdown.