Update 0.13.x release branch for 0.13.7
This MR merges the changes from the following MRs onto the release/0.13.x branch to finalise the 0.13.7 release:
- !505 (merged)
- !665 (merged)
- !666 (merged)
- !668 (merged)
- !675 (merged)
- !676 (merged)
- !682 (merged)
- !684 (merged)
- !686 (merged)
- !689 (merged)
- !700 (merged)
This release a) updates pesummary to be compatible with Python >= 3.8, <= 3.10, b) updates the testing suite to run on multiple CPUs, c) deprecates setup.py install and d) updates scipy >= 1.8.0