find and replace keywords with urls ONLY if not already wrapped in a url
<p>So, I can easily do this:</p>

<pre><code>$keywords = array(' jacket ',' sweater ',);
$urls = array(' &lt;a href="#"&gt;jacket&lt;/a&gt; ',' &lt;a href="#"&gt;sweater&lt;/a&gt; ',);
$content = str_ireplace($keywords,$urls,$content);
</code></pre>

<p>But the problem is when something like jacket or sweater is already in a link tag.</p>

<p>I can't think of any simple solutions to this...</p>
