DOC: clarify interp1d 'zero' argument
DOC: clarify interp1d 'zero' argument

Clarify that the interp1d 'zero' arguments means interpolation with
a zero order spline, i.e. a piecewise constant function interpolating
to the most recently observed value.

aarchiba/scipy,andyfaff/scipy,anntzer/scipy,zerothi/scipy,arokem/scipy,zerothi/scipy,Eric89GXL/scipy,ilayn/scipy,josephcslater/scipy,vigna/scipy,WarrenWeckesser/scipy,grlee77/scipy,mdhaber/scipy,jor-/scipy,WarrenWeckesser/scipy,befelix/scipy,gertingold/scipy,matthew-brett/scipy,jakevdp/scipy,person142/scipy,pschella/scipy,Stefan-Endres/scipy,scipy/scipy,jamestwebber/scipy,gertingold/scipy,pizzathief/scipy,perimosocordiae/scipy,endolith/scipy,person142/scipy,e-q/scipy,anntzer/scipy,WarrenWeckesser/scipy,tylerjereddy/scipy,nmayorov/scipy,scipy/scipy,befelix/scipy,pizzathief/scipy,perimosocordiae/scipy,gertingold/scipy,matthew-brett/scipy,grlee77/scipy,perimosocordiae/scipy,rgommers/scipy,nmayorov/scipy,jor-/scipy,ilayn/scipy,jjhelmus/scipy,ilayn/scipy,jamestwebber/scipy,mdhaber/scipy,jjhelmus/scipy,gertingold/scipy,mdhaber/scipy,endolith/scipy,tylerjereddy/scipy,scipy/scipy,aeklant/scipy,Eric89GXL/scipy,jakevdp/scipy,jor-/scipy,jjhelmus/scipy,pbrod/scipy,scipy/scipy,aeklant/scipy,aarchiba/scipy,jor-/scipy,gfyoung/scipy,zerothi/scipy,arokem/scipy,gfyoung/scipy,befelix/scipy,jor-/scipy,vigna/scipy,Stefan-Endres/scipy,apbard/scipy,nmayorov/scipy,pbrod/scipy,person142/scipy,dominicelse/scipy,perimosocordiae/scipy,josephcslater/scipy,vigna/scipy,pschella/scipy,andyfaff/scipy,aeklant/scipy,scipy/scipy,e-q/scipy,nmayorov/scipy,befelix/scipy,aeklant/scipy,matthew-brett/scipy,anntzer/scipy,rgommers/scipy,Stefan-Endres/scipy,jamestwebber/scipy,gfyoung/scipy,endolith/scipy,pschella/scipy,gfyoung/scipy,ilayn/scipy,pschella/scipy,tylerjereddy/scipy,Stefan-Endres/scipy,zerothi/scipy,ilayn/scipy,jakevdp/scipy,lhilt/scipy,pizzathief/scipy,endolith/scipy,aeklant/scipy,apbard/scipy,jamestwebber/scipy,arokem/scipy,e-q/scipy,gertingold/scipy,Eric89GXL/scipy,Stefan-Endres/scipy,rgommers/scipy,aarchiba/scipy,pbrod/scipy,apbard/scipy,jakevdp/scipy,grlee77/scipy,pizzathief/scipy,perimosocordiae/scipy,gfyoung/scipy,befelix/scipy,arokem/scipy,Eric89GXL/scipy,apbard/scipy,vigna/scipy,arokem/scipy,pizzathief/scipy,anntzer/scipy,endolith/scipy,andyfaff/scipy,jjhelmus/scipy,dominicelse/scipy,WarrenWeckesser/scipy,andyfaff/scipy,dominicelse/scipy,Stefan-Endres/scipy,lhilt/scipy,WarrenWeckesser/scipy,endolith/scipy,person142/scipy,rgommers/scipy,vigna/scipy,mdhaber/scipy,jakevdp/scipy,Eric89GXL/scipy,Eric89GXL/scipy,matthew-brett/scipy,jamestwebber/scipy,jjhelmus/scipy,pbrod/scipy,andyfaff/scipy,josephcslater/scipy,perimosocordiae/scipy,e-q/scipy,andyfaff/scipy,dominicelse/scipy,mdhaber/scipy,lhilt/scipy,dominicelse/scipy,pbrod/scipy,tylerjereddy/scipy,tylerjereddy/scipy,grlee77/scipy,anntzer/scipy,scipy/scipy,lhilt/scipy,grlee77/scipy,rgommers/scipy,pschella/scipy,lhilt/scipy,mdhaber/scipy,josephcslater/scipy,josephcslater/scipy,WarrenWeckesser/scipy,aarchiba/scipy,zerothi/scipy,zerothi/scipy,pbrod/scipy,ilayn/scipy,aarchiba/scipy,matthew-brett/scipy,nmayorov/scipy,apbard/scipy,person142/scipy,anntzer/scipy,e-q/scipy