How to specify metadata for dask.dataframe
<p>The docs provide good examples, <a href="http://dask.pydata.org/en/latest/dataframe-design.html#metadata" rel="noreferrer">how metadata can be provided</a>. However I still feel unsure, when it comes to picking the right dtypes for my dataframe.</p>

<ul>
<li>Could I do something like <code>meta={'x': int 'y': float,
'z': float}</code> instead of <code>meta={'x': 'i8', 'y': 'f8', 'z': 'f8'}</code>?</li>
<li>Could somebody hint me to a list of possible values like 'i8'?  What
dtypes exist? </li>
<li>How    can I specify a column, that contains arbitrary objects? How can I    specify a column, that contains only instances of one class?</li>
</ul>