Added documentation and script to plot butterfly
Merge branch '1051-create-ctbutterfly' of https://cta-git.irap.omp.eu/ctools into 1051-create-ctbutterfly
ctselect now respects any pre-existing energy or ROI cut. It automatically adjusts the intervals, leading in the worst case to an empty event list if no overlap exists.
Do some minor corrections.
Install show_butterfly.py.
Merge branch '1051-create-ctbutterfly' into integration
Install pipeline_stacked_mem.py script in examples folder.
Correct typo
Correct path name in documentation