fix: use autolinks for URLs that contain an ampersand

The link text goes through TextConverter, which escapes `&` to `&`,
while the href is the decoded attribute value, so `$href === $text` never
held for a URL with a query string like `?a=1&b=2`. Undo that escaping
before comparing. Only `&amp;` is undone: `<` and `>` cannot appear in an
autolink, so those links keep the inline form.

Fixes #248

src/Converter/LinkConverter.php

@@ -26,7 +26,7 @@ class LinkConverter implements ConverterInterface, ConfigurationAwareInterface
 
         if ($title !== '') {
             $markdown = '[' . $text . '](' . $href . ' "' . $title . '")';
-        } elseif ($href === $text && $this->isValidAutolink($href)) {
+        } elseif ($href === \str_replace('&', '&', $text) && $this->isValidAutolink($href)) {
             $markdown = '<' . $href . '>';
         } elseif ($href === 'mailto:' . $text && $this->isValidEmail($text)) {
             $markdown = '<' . $text . '>';