add tests for codespans with backticks in them

Author: Feder1co5oave

test/new/nested_code.html

@@ -1 +1,9 @@
 <p><code>hi ther `` ok ```</code></p>
+
+<p><code>`</code></p>
+
+<p><code>There is a literal backtick (`) here.</code></p>
+
+<p>A backtick-delimited string in a code span: <code>`foo`</code></p>
+
+<p>Please don&#39;t use any <code>&lt;blink&gt;</code> tags.</p>

test/new/nested_code.md

@@ -1 +1,9 @@
 ````` hi ther `` ok ``` `````
+
+`` ` ``
+
+``There is a literal backtick (`) here.``
+
+A backtick-delimited string in a code span: `` `foo` ``
+
+Please don't use any `<blink>` tags.