Fix nested footnotes

This is both nasty and neat at the same time. All the code could handle
nested footnotes just fine, the only place that was not working was the
final loop that printed the list. The loop was in a range form, which
couldn't account for another footnote being inserted while processing
existing ones. Changing the loop to the iterative form solves that.

Closes #193.

inline_test.go

@@ -1000,6 +1000,33 @@ func TestFootnotesWithParameters(t *testing.T) {
 	doTestsInlineParam(t, tests, Options{Extensions: EXTENSION_FOOTNOTES}, HTML_FOOTNOTE_RETURN_LINKS, params)
 }
 
+func TestNestedFootnotes(t *testing.T) {
+	var tests = []string{
+		`Paragraph.[^fn1]
+
+[^fn1]:
+  Asterisk[^fn2]
+
+[^fn2]:
+  Obelisk`,
+		`<p>Paragraph.<sup class="footnote-ref" id="fnref:fn1"><a rel="footnote" href="#fn:fn1">1</a></sup></p>
+<div class="footnotes">
+
+<hr />
+
+<ol>
+<li id="fn:fn1">Asterisk<sup class="footnote-ref" id="fnref:fn2"><a rel="footnote" href="#fn:fn2">2</a></sup>
+</li>
+<li id="fn:fn2">Obelisk
+</li>
+</ol>
+</div>
+`,
+	}
+	doTestsInlineParam(t, tests, Options{Extensions: EXTENSION_FOOTNOTES}, 0,
+		HtmlRendererParameters{})
+}
+
 func TestInlineComments(t *testing.T) {
 	var tests = []string{
 		"Hello <!-- there ->\n",

markdown.go

@@ -452,8 +452,9 @@ func secondPass(p *parser, input []byte) []byte {
 	if p.flags&EXTENSION_FOOTNOTES != 0 && len(p.notes) > 0 {
 		p.r.Footnotes(&output, func() bool {
 			flags := LIST_ITEM_BEGINNING_OF_LIST
-			for _, ref := range p.notes {
+			for i := 0; i < len(p.notes); i += 1 {
 				var buf bytes.Buffer
+				ref := p.notes[i]
 				if ref.hasBlock {
 					flags |= LIST_ITEM_CONTAINS_BLOCK
 					p.block(&buf, ref.title)