Warnings if there is a bias in timings due to some side-effects of the method
Include "worst timings" from the tuning to find number of runs
FIX: Zero Division Error
Better and more explicit warning message
Add a small line to whatsnew.rst
Merge pull request #6479 from MechCoder/timeit_warning

Warnings if there is a bias in timings due to some side-effects of the method