rollback change to footnote names

invalidating spaces in footnote names, while technically correct from
HTML standards point of view is an unnecessarily burdensome breaking
change at this time

Michelf/MarkdownExtra.php

@@ -1645,7 +1645,7 @@ class MarkdownExtra extends \Michelf\Markdown {
 	 */
 	protected function doFootnotes($text) {
 		if (!$this->in_anchor) {
-			$text = preg_replace('{\[\^(\S+?)\]}', "F\x1Afn:\\1\x1A:", $text);
+			$text = preg_replace('{\[\^(.+?)\]}', "F\x1Afn:\\1\x1A:", $text);
 		}
 		return $text;
 	}

test/resources/php-markdown-extra.mdtest/Footnotes.text

@@ -68,9 +68,3 @@ Footnotes mixed with images[^image-mixed]
 [img6]: images/MGR-1800-travel.jpeg "Travel Speeds in 1800"
 [^image-mixed]: Footnote Content
 [img7]: images/MGR-1830-travel.jpeg "Travel Speeds in 1830"
-
- - - -
-
-This is not a valid footnote name because it has whitespace.[^invalid fn]
-
-[^invalid fn]: an invalid footnote name

test/resources/php-markdown-extra.mdtest/Footnotes.xhtml

@@ -30,10 +30,6 @@ footnote test<sup id="fnref:reference"><a href="#fn:reference" class="footnote-r
 
 <p>Footnotes mixed with images<sup id="fnref:image-mixed"><a class="footnote-ref" role="doc-noteref" href="#fn:image-mixed">11</a></sup><img alt="1800 Travel" src="images/MGR-1800-travel.jpeg" title="Travel Speeds in 1800"/><img alt="1830 Travel" src="images/MGR-1830-travel.jpeg" title="Travel Speeds in 1830"/></p>
 
-<hr/>
-
-<p>This is not a valid footnote name because it has whitespace.[^invalid fn]</p>
-
 <div class="footnotes" role="doc-endnotes">
 <hr />
 <ol>