#362 Sample operation initial work

Initial version of Sample() operation implemented and tested for numpy and pandas.
Sample() should randomly select some items from a given datasource and return them.
For numpy and pandas, the returned data are new arrays or dataframes or series.

I don't think these kind of javadoc style params will get picked up by sphinx, but maybe they will...

i htink the convention is to use the numpy doc style

https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt#sections