downlit 0.2.0

• Autolinking can use metadata stored in package itself with pkgdown setting
  deploy.install_metadata; this is useful for packages that only have
  private websites (@matthewstrasiotto, #29)

• Autolinking guesses reference and article urls for pkgdown sites that haven't
  set url (@krlmlr, #44).

• R6 classes are autolinked when a new object is created i.e. in
  r6_object$new(), r6_object will link to its docs (#59, @maelle).

• R6 methods are no longer autolinked as if they were functions of the same
  name (#54, @maelle).

• classes_pandoc() and classes_chroma() have been thoroughly revieweed to
  produce syntax highlighting as similar as possible to RStudio.

• downlit_html_path() has a more flexible XPath identifying R code blocks,
  and a classes argument (#53, @maelle, @cderv)

• Trailing / are no longer stripped from URLs (#45, @krlmlr).

• Removed extra newline in <pre> output (#42, @krlmlr).