REL: add `python_requires` to setup.py, fix Python version check. (#7313)
REL: add `python_requires` to setup.py, fix Python version check. (#7313)

This allows pip to figure out the last compatible version
with a particular Python version before attempting to
install.

Support for this field was added to setuptools last year:
https://github.com/pypa/setuptools/pull/631
befelix/scipy,anntzer/scipy,josephcslater/scipy,grlee77/scipy,lhilt/scipy,lhilt/scipy,aeklant/scipy,matthew-brett/scipy,rgommers/scipy,tylerjereddy/scipy,vigna/scipy,pbrod/scipy,anntzer/scipy,arokem/scipy,nmayorov/scipy,rgommers/scipy,apbard/scipy,apbard/scipy,pizzathief/scipy,grlee77/scipy,scipy/scipy,jjhelmus/scipy,anntzer/scipy,pbrod/scipy,zerothi/scipy,Eric89GXL/scipy,zerothi/scipy,josephcslater/scipy,scipy/scipy,perimosocordiae/scipy,scipy/scipy,aarchiba/scipy,scipy/scipy,perimosocordiae/scipy,andyfaff/scipy,pizzathief/scipy,josephcslater/scipy,aeklant/scipy,vigna/scipy,tylerjereddy/scipy,jakevdp/scipy,jor-/scipy,Eric89GXL/scipy,Stefan-Endres/scipy,aeklant/scipy,jjhelmus/scipy,nmayorov/scipy,arokem/scipy,aarchiba/scipy,nmayorov/scipy,jakevdp/scipy,ilayn/scipy,Eric89GXL/scipy,arokem/scipy,gfyoung/scipy,nmayorov/scipy,befelix/scipy,pbrod/scipy,jakevdp/scipy,rgommers/scipy,e-q/scipy,jamestwebber/scipy,gfyoung/scipy,endolith/scipy,lhilt/scipy,jakevdp/scipy,endolith/scipy,perimosocordiae/scipy,andyfaff/scipy,pbrod/scipy,pizzathief/scipy,jakevdp/scipy,andyfaff/scipy,grlee77/scipy,andyfaff/scipy,zerothi/scipy,aeklant/scipy,Stefan-Endres/scipy,apbard/scipy,andyfaff/scipy,vigna/scipy,pizzathief/scipy,jamestwebber/scipy,Stefan-Endres/scipy,gfyoung/scipy,apbard/scipy,jamestwebber/scipy,Stefan-Endres/scipy,Stefan-Endres/scipy,e-q/scipy,zerothi/scipy,befelix/scipy,zerothi/scipy,aarchiba/scipy,tylerjereddy/scipy,matthew-brett/scipy,pbrod/scipy,jjhelmus/scipy,gertingold/scipy,ilayn/scipy,befelix/scipy,endolith/scipy,gertingold/scipy,gertingold/scipy,jamestwebber/scipy,endolith/scipy,pizzathief/scipy,nmayorov/scipy,matthew-brett/scipy,grlee77/scipy,anntzer/scipy,e-q/scipy,ilayn/scipy,aarchiba/scipy,person142/scipy,josephcslater/scipy,aeklant/scipy,perimosocordiae/scipy,scipy/scipy,Stefan-Endres/scipy,vigna/scipy,matthew-brett/scipy,scipy/scipy,anntzer/scipy,mdhaber/scipy,arokem/scipy,vigna/scipy,perimosocordiae/scipy,Eric89GXL/scipy,mdhaber/scipy,jor-/scipy,befelix/scipy,gfyoung/scipy,mdhaber/scipy,WarrenWeckesser/scipy,WarrenWeckesser/scipy,anntzer/scipy,arokem/scipy,e-q/scipy,WarrenWeckesser/scipy,rgommers/scipy,person142/scipy,mdhaber/scipy,mdhaber/scipy,jjhelmus/scipy,gertingold/scipy,jor-/scipy,endolith/scipy,rgommers/scipy,mdhaber/scipy,jjhelmus/scipy,lhilt/scipy,WarrenWeckesser/scipy,ilayn/scipy,tylerjereddy/scipy,Eric89GXL/scipy,pbrod/scipy,josephcslater/scipy,grlee77/scipy,Eric89GXL/scipy,perimosocordiae/scipy,gfyoung/scipy,jor-/scipy,andyfaff/scipy,tylerjereddy/scipy,gertingold/scipy,WarrenWeckesser/scipy,person142/scipy,e-q/scipy,jor-/scipy,lhilt/scipy,zerothi/scipy,aarchiba/scipy,matthew-brett/scipy,jamestwebber/scipy,ilayn/scipy,person142/scipy,apbard/scipy,WarrenWeckesser/scipy,person142/scipy,ilayn/scipy,endolith/scipy