BColz

BColz computational backend.  Like the new PyTables backend this is pretty minimal.  It defaults to using the Python backend.  It does provide a nice interface though. 

* [Notebook demo](https://gist.github.com/mrocklin/59df551f1b282aef9932)
* [nbviewer link](http://nbviewer.ipython.org/gist/mrocklin/59df551f1b282aef9932)

cc @FrancescAlted .  I know you've moved on from Blaze but I thought that this might interest you from a `bcolz` perspective.  The uniformity of the Blaze interface might lower barriers for some users to move to more efficient but less predominant backends like bcolz.

This is a WIP.  There are no tests and I should add `into` implementations.  Still, it's simple enough to be encouraging.

This also builds off of a couple other PRs so you may want to step around the numpy and pytables stuff.  The relevant file is [bcolz.py](https://github.com/mrocklin/blaze/blob/bcolz/blaze/compute/bcolz.py)