DOC: forward port 1.8.0 relnotes
DOC: forward port 1.8.0 relnotes

* forward port the SciPy `1.8.0` release notes
following the final release

endolith/scipy,WarrenWeckesser/scipy,scipy/scipy,anntzer/scipy,ilayn/scipy,mdhaber/scipy,mdhaber/scipy,scipy/scipy,ilayn/scipy,WarrenWeckesser/scipy,ilayn/scipy,perimosocordiae/scipy,anntzer/scipy,Stefan-Endres/scipy,WarrenWeckesser/scipy,WarrenWeckesser/scipy,endolith/scipy,scipy/scipy,mdhaber/scipy,Stefan-Endres/scipy,WarrenWeckesser/scipy,perimosocordiae/scipy,endolith/scipy,vigna/scipy,vigna/scipy,Stefan-Endres/scipy,rgommers/scipy,scipy/scipy,mdhaber/scipy,ilayn/scipy,anntzer/scipy,rgommers/scipy,perimosocordiae/scipy,perimosocordiae/scipy,scipy/scipy,Stefan-Endres/scipy,ilayn/scipy,andyfaff/scipy,ilayn/scipy,scipy/scipy,andyfaff/scipy,vigna/scipy,Stefan-Endres/scipy,andyfaff/scipy,perimosocordiae/scipy,vigna/scipy,anntzer/scipy,rgommers/scipy,perimosocordiae/scipy,mdhaber/scipy,mdhaber/scipy,andyfaff/scipy,rgommers/scipy,endolith/scipy,andyfaff/scipy,anntzer/scipy,Stefan-Endres/scipy,vigna/scipy,andyfaff/scipy,WarrenWeckesser/scipy,endolith/scipy,endolith/scipy,rgommers/scipy,anntzer/scipy