Added statement about BivariateSpline being an abstract base class
Added statement about BivariateSpline being an abstract base class

Closes #2262.
cpaulik/scipy,aeklant/scipy,zaxliu/scipy,Newman101/scipy,sonnyhu/scipy,newemailjdm/scipy,e-q/scipy,befelix/scipy,gdooper/scipy,gertingold/scipy,Gillu13/scipy,pschella/scipy,haudren/scipy,jor-/scipy,jamestwebber/scipy,juliantaylor/scipy,newemailjdm/scipy,jonycgn/scipy,jsilter/scipy,mortada/scipy,chatcannon/scipy,gef756/scipy,matthew-brett/scipy,Shaswat27/scipy,mikebenfield/scipy,pyramania/scipy,vanpact/scipy,WarrenWeckesser/scipy,mingwpy/scipy,efiring/scipy,piyush0609/scipy,Newman101/scipy,maciejkula/scipy,anntzer/scipy,raoulbq/scipy,jseabold/scipy,Kamp9/scipy,trankmichael/scipy,befelix/scipy,newemailjdm/scipy,endolith/scipy,arokem/scipy,newemailjdm/scipy,FRidh/scipy,scipy/scipy,Shaswat27/scipy,nmayorov/scipy,befelix/scipy,petebachant/scipy,futurulus/scipy,vberaudi/scipy,efiring/scipy,nonhermitian/scipy,perimosocordiae/scipy,Srisai85/scipy,scipy/scipy,fernand/scipy,e-q/scipy,futurulus/scipy,ales-erjavec/scipy,nonhermitian/scipy,piyush0609/scipy,WarrenWeckesser/scipy,larsmans/scipy,Eric89GXL/scipy,ortylp/scipy,juliantaylor/scipy,maniteja123/scipy,maniteja123/scipy,njwilson23/scipy,gfyoung/scipy,aarchiba/scipy,raoulbq/scipy,scipy/scipy,kleskjr/scipy,larsmans/scipy,giorgiop/scipy,zxsted/scipy,giorgiop/scipy,surhudm/scipy,niknow/scipy,njwilson23/scipy,witcxc/scipy,mortonjt/scipy,raoulbq/scipy,argriffing/scipy,behzadnouri/scipy,mtrbean/scipy,anielsen001/scipy,lhilt/scipy,mtrbean/scipy,jakevdp/scipy,andyfaff/scipy,Gillu13/scipy,aeklant/scipy,woodscn/scipy,ogrisel/scipy,mgaitan/scipy,mhogg/scipy,minhlongdo/scipy,mgaitan/scipy,Srisai85/scipy,haudren/scipy,mortada/scipy,tylerjereddy/scipy,richardotis/scipy,WillieMaddox/scipy,apbard/scipy,petebachant/scipy,vigna/scipy,aman-iitj/scipy,felipebetancur/scipy,aarchiba/scipy,lhilt/scipy,rgommers/scipy,cpaulik/scipy,pyramania/scipy,Dapid/scipy,jsilter/scipy,rmcgibbo/scipy,ndchorley/scipy,behzadnouri/scipy,ales-erjavec/scipy,surhudm/scipy,lukauskas/scipy,anielsen001/scipy,mortada/scipy,pschella/scipy,zerothi/scipy,Newman101/scipy,efiring/scipy,niknow/scipy,andyfaff/scipy,bkendzior/scipy,WarrenWeckesser/scipy,Kamp9/scipy,fernand/scipy,gdooper/scipy,andyfaff/scipy,WarrenWeckesser/scipy,minhlongdo/scipy,dch312/scipy,WillieMaddox/scipy,futurulus/scipy,fernand/scipy,nonhermitian/scipy,jakevdp/scipy,gef756/scipy,perimosocordiae/scipy,sriki18/scipy,anntzer/scipy,larsmans/scipy,maniteja123/scipy,dominicelse/scipy,fernand/scipy,andyfaff/scipy,mhogg/scipy,hainm/scipy,matthewalbani/scipy,juliantaylor/scipy,lhilt/scipy,petebachant/scipy,ales-erjavec/scipy,ogrisel/scipy,perimosocordiae/scipy,Kamp9/scipy,befelix/scipy,woodscn/scipy,mgaitan/scipy,anielsen001/scipy,mingwpy/scipy,raoulbq/scipy,minhlongdo/scipy,andyfaff/scipy,rgommers/scipy,vhaasteren/scipy,woodscn/scipy,zerothi/scipy,petebachant/scipy,sriki18/scipy,sonnyhu/scipy,felipebetancur/scipy,gertingold/scipy,sauliusl/scipy,juliantaylor/scipy,pbrod/scipy,witcxc/scipy,endolith/scipy,vigna/scipy,kleskjr/scipy,vberaudi/scipy,gfyoung/scipy,jakevdp/scipy,niknow/scipy,ndchorley/scipy,josephcslater/scipy,jseabold/scipy,mortada/scipy,WillieMaddox/scipy,ilayn/scipy,vanpact/scipy,apbard/scipy,nmayorov/scipy,richardotis/scipy,aeklant/scipy,mtrbean/scipy,apbard/scipy,mikebenfield/scipy,Shaswat27/scipy,Stefan-Endres/scipy,ortylp/scipy,pnedunuri/scipy,Eric89GXL/scipy,jonycgn/scipy,nonhermitian/scipy,mdhaber/scipy,ChanderG/scipy,FRidh/scipy,arokem/scipy,kalvdans/scipy,nvoron23/scipy,lukauskas/scipy,FRidh/scipy,zerothi/scipy,woodscn/scipy,matthewalbani/scipy,jonycgn/scipy,vanpact/scipy,ChanderG/scipy,aeklant/scipy,WarrenWeckesser/scipy,jjhelmus/scipy,sauliusl/scipy,ilayn/scipy,aman-iitj/scipy,rmcgibbo/scipy,behzadnouri/scipy,aman-iitj/scipy,haudren/scipy,mikebenfield/scipy,gfyoung/scipy,pnedunuri/scipy,ChanderG/scipy,vhaasteren/scipy,Gillu13/scipy,sauliusl/scipy,rmcgibbo/scipy,zaxliu/scipy,pbrod/scipy,niknow/scipy,josephcslater/scipy,larsmans/scipy,lukauskas/scipy,behzadnouri/scipy,mdhaber/scipy,kalvdans/scipy,ortylp/scipy,mtrbean/scipy,zerothi/scipy,niknow/scipy,andyfaff/scipy,vanpact/scipy,fredrikw/scipy,Newman101/scipy,ortylp/scipy,kleskjr/scipy,dominicelse/scipy,trankmichael/scipy,jsilter/scipy,trankmichael/scipy,mortada/scipy,chatcannon/scipy,perimosocordiae/scipy,jjhelmus/scipy,zaxliu/scipy,efiring/scipy,bkendzior/scipy,ortylp/scipy,sriki18/scipy,jamestwebber/scipy,ndchorley/scipy,Kamp9/scipy,nonhermitian/scipy,argriffing/scipy,befelix/scipy,gfyoung/scipy,kalvdans/scipy,ilayn/scipy,mtrbean/scipy,kleskjr/scipy,mingwpy/scipy,Srisai85/scipy,pbrod/scipy,Newman101/scipy,mdhaber/scipy,hainm/scipy,anielsen001/scipy,zxsted/scipy,surhudm/scipy,richardotis/scipy,jamestwebber/scipy,njwilson23/scipy,Eric89GXL/scipy,chatcannon/scipy,zerothi/scipy,Srisai85/scipy,tylerjereddy/scipy,pschella/scipy,gef756/scipy,endolith/scipy,grlee77/scipy,rgommers/scipy,gdooper/scipy,mtrbean/scipy,WillieMaddox/scipy,mortonjt/scipy,e-q/scipy,pizzathief/scipy,FRidh/scipy,lukauskas/scipy,andim/scipy,gef756/scipy,gef756/scipy,pnedunuri/scipy,haudren/scipy,sonnyhu/scipy,fernand/scip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