This Pull request:

• Functions to create and fill Histograms objects with numpy arrays
• Function to retrieve Numpy arrays from histograms and graphs
• Functions to create TGraph's object from numpy using TGraph constructor
• UHI indexing and slice

To be added yet:

• Refactored code for methods
• Testing each implementation
• Tests in the test directory for each implementation

Changes or fixes:

Checklist:

• tested changes locally
• updated the docs (if necessary)

This PR fixes #