Date extraction support

[mish15]

Can this library extract dates? Seems article{} has the parameter, but maybe it's not supported yet?

Some examples of how dates appear in meta:

<meta content="2014-06-16T06:01:15.750Z" property="article:published_time"/>

<meta content="2014-06-16T06:01:15.750Z" property="article:modified_time"/>

<span>
<time class="articlepublishdate" datetime="2015-09-04" itemprop="datePublished">4 September, 2015
</span>

<meta itemprop="datePublished" content="2009-05-08">