Wrap footnote definition in a paragraph

Closes GH-14.
Closes GH-15.

Amended-by: Titus Wormer <[email protected]>

Author: vhf

lib/handlers/footnote.js

@@ -25,7 +25,10 @@ function footnote(h, node) {
   footnotes.push({
     type: 'footnoteDefinition',
     identifier: identifier,
-    children: node.children,
+    children: [{
+      type: 'paragraph',
+      children: node.children
+    }],
     position: node.position
   });
 

test/footnote.js

@@ -33,7 +33,7 @@ test('Footnote', function (t) {
             properties: {id: 'fn-1'}
           }, [
             u('text', '\n'),
-            u('text', 'bravo'),
+            u('element', {tagName: 'p', properties: {}}, [u('text', 'bravo')]),
             u('text', '\n'),
             u('element', {
               tagName: 'a',
@@ -108,7 +108,7 @@ test('Footnote', function (t) {
             properties: {id: 'fn-2'}
           }, [
             u('text', '\n'),
-            u('text', 'charlie'),
+            u('element', {tagName: 'p', properties: {}}, [u('text', 'charlie')]),
             u('text', '\n'),
             u('element', {
               tagName: 'a',