Vectorizing histogramming (collections)

[kreczko]

While it is possible to fill histograms, it is currently impossible to select the bins in a vectorized way.

E.g. a vectorized processing with a batch_size of 10000 will have

len(event.pileup) == 1000

when selecting the correct bins the corresponding functions, e.g. _get_pu_bin need to handle array input:

pileupBins=[0,10,15,20,30,999]

_get_pu_bin(23) # --> 3

_get_pu_bin([12, 23, 33]) # --> [1, 3, 4]

[kreczko]

@benkrikler related to #39?