test adding integers

python_arithmetic.py added for element PythonAddition()
Python arithmetic : subtraction
Python arithmetic : multiplication
Python arithmetic : true division
Python arithmetic : modulo
Python arithmetic : exponentiation
Python arithmetic : floor division

logic/python_arithmetic.py
--> add PythonFloorDivision() element
--> delete copy/pasted comments that make no sense

test/test_flow_logic.py
--> add test_dividing_integers_with_floor_division()
--> change last modulo test to divide by -0.1 and accept 2 results: 0.0 and -0.1
remove "Python arithmetic" from TODO list
Merge branch 'feature/python_arithmetic_operators' into develop