Angle quotes again :)

With 0.17.3, the following angle quotes are not handled ideally

```
 Source: "<<test>>abcd<</test1>>"
 Flexmark:
 &laquo;test&raquo;abcd&lt;&lt;/test1&gt;&gt;
 Pegdown:
 &laquo;test&raquo;abcd&laquo;/test1&raquo;

 Source: <<test>>abcd<<:test1>>"
 Flexmark:
 &laquo;test&raquo;abcd&lt;&lt;:test1&gt;&gt;
 Pegdown:
 &laquo;test&raquo;abcd&laquo;:test1&raquo;
```