WIP: add FillHistogram and automatic binning (first implementation)

This branch introduces a new free function:

FillHistogram(data, *args, **kwargs)

the interesting point is the "binning" argument wich allow you to specify a particular method to automatically choose a binning for 1D histograms.

Have a look to the example

examples/plotting/fill_hist.py

here a screenshot of the result.

![autobinning](https://f.cloud.github.com/assets/143389/350555/3a7e8aec-a023-11e2-8cbb-8ca5f06e1270.png)

The implentation is not complete, I am asking for your feedback: for example is it ok to use free functions? Do you prefer a method? ...

Christoph told me Noel already implemented filling of histograms from numpy arrays. Where is it?



Cheers,
Ruggero