nitdoc: Escape URLs.

Signed-off-by: Jean-Christophe Beaupré <jcbrinfo@users.noreply.github.com>
nitdoc: Escape headers.

Signed-off-by: Jean-Christophe Beaupré <jcbrinfo@users.noreply.github.com>
nitdoc: Escape attributes.

Signed-off-by: Jean-Christophe Beaupré <jcbrinfo@users.noreply.github.com>