unexpanded &lt; &gt; &amp;

From: https://bugs.debian.org/791470

Version: 2015.6.21-1 (and current master):

``` console
$ echo '<body>&lt;&gt;&amp;</body>' | html2markdown
&lt;&gt;&amp;
```

It worked correctly in 2014.9.25-1:

``` console
$ echo '<body>&lt;&gt;&amp;</body>' | html2markdown
<>&
```
