Adding the function "find_sudden_changes.py" on utils.py - Adding the first pytest for the function in test_utils.py

Added the function find_sudden_changes.py. It can find the discontinuities, however the user should play a bit with p0 and the detrending. If the discontinuity is not that obvious, it may not find it, even if it can be seen by eye. Added a folder tests, for all the future pytests. Inside, there is the file test_utils.py where I put the first pytest, testing the added function. Also, inside the folder tests, there is another folder called data_tests which contains one data with points x y and their errors, to be used to the pytest. The idea is for the folder to contain all future simple data files that would be used for other pytests.