Autofill empty labels in Markdown links
Autofill empty labels in Markdown links

- as_text() is now a function that takes the session as an argument
- likewise as_html(), which also takes URL makers and the language
- since there should be only one link extension, it is registered by
  setting default_link_extension, not appending to markdown_extensions.
  This only affects the __html__ attribute.

xfix/pokedex,RK905/pokedex-1,veekun/pokedex,DaMouse404/pokedex,mschex1/pokedex,veekun/pokedex