#4

Now HistogramSysTest.HistoPlot accepts either a numpy ndarray or a list of ndarray as input, and will overplot the histograms together is multiple datasets are provided.  

Weighted-histogram is also allowed.

![gaussian_test_1](https://cloud.githubusercontent.com/assets/7539807/4351306/ea0b5368-4208-11e4-9af4-c86d1b1ad67f.png)
![gaussian_test_2](https://cloud.githubusercontent.com/assets/7539807/4351307/ea172620-4208-11e4-90ae-9084e2f6a9f9.png)
![gaussian_test_3](https://cloud.githubusercontent.com/assets/7539807/4351308/ea190bc0-4208-11e4-9638-2d62a90a996e.png)



Also, you should say that this can also be a list of styles if you have multiple items in `data_list`, as long as the lists have the same length.  (Ditto for all the options below where this is true.  It's cool that there are so many of them!)