ENH: Add Emperor class

This class allows an IPython notebook user to display PCoA plots inline and
without struggle. Note that at the moment this object does not support all
the functionality that make_emperor.py does, this will require further
work in the overall structure of the script code. However, it would be super
useful if people started trying this out and pointed out the things that are
the most needed at the moment.

See this notebook (note that NBViewer does some weird things so it is better
to download this notebook and try it on your own):
http://nbviewer.ipython.org/gist/ElDeveloper/24a383b778943a187966

In case you cannot try the notebook, see this image:

![](http://i.imgur.com/PfgqU0J.png)

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HT to the IPython developers that helped me figure this out at SciPy last week
the solution ended up being really nice and provides (I think) a really easy to
use object.
We are not there yet, though I suspect that we'll get there in the next release (but shhhhhh, it is supposed to be a surprise :speak_no_evil: ).