feat(library/data/list/set): add decidable_nodup
feat(library/data/list/set): add decidable_nodup

rlewis1988/lean,leanprover/lean,leanprover-community/lean,soonhokong/lean-osx,leodemoura/lean,Kha/lean,c-cube/lean,digama0/lean,sp3ctum/lean,soonhokong/lean,htzh/lean,digama0/lean,leanprover/lean,soonhokong/lean-windows,avigad/lean,johoelzl/lean,leanprover-community/lean,dselsam/lean,soonhokong/lean,soonhokong/lean,javra/lean,Kha/lean,UlrikBuchholtz/lean,UlrikBuchholtz/lean,sp3ctum/lean,rlewis1988/lean,leodemoura/lean,avigad/lean,soonhokong/lean-osx,johoelzl/lean,c-cube/lean,soonhokong/lean-windows,UlrikBuchholtz/lean,Kha/lean,UlrikBuchholtz/lean,soonhokong/lean-osx,leanprover/lean,javra/lean,fpvandoorn/lean2,dselsam/lean,c-cube/lean,fgdorais/lean,fpvandoorn/lean,sp3ctum/lean,Kha/lean,levnach/lean,fpvandoorn/lean2,fpvandoorn/lean,fgdorais/lean,soonhokong/lean-windows,fgdorais/lean,levnach/lean,fgdorais/lean,eigengrau/lean,leanprover-community/lean,avigad/lean,leodemoura/lean,Kha/lean,leanprover/lean,levnach/lean,eigengrau/lean,fgdorais/lean,johoelzl/lean,leodemoura/lean,leanprover-community/lean,johoelzl/lean,fpvandoorn/lean,johoelzl/lean,dselsam/lean,leanprover-community/lean,fgdorais/lean,leanprover/lean,dselsam/lean,avigad/lean,htzh/lean,c-cube/lean,fpvandoorn/lean2,rlewis1988/lean,levnach/lean,sp3ctum/lean,eigengrau/lean,javra/lean,Kha/lean,rlewis1988/lean,digama0/lean,eigengrau/lean,htzh/lean,htzh/lean,fpvandoorn/lean,soonhokong/lean-windows,levnach/lean,soonhokong/lean,leanprover-community/lean,rlewis1988/lean,avigad/lean,javra/lean,leodemoura/lean,fpvandoorn/lean,soonhokong/lean-windows,soonhokong/lean-osx,fpvandoorn/lean2,javra/lean,htzh/lean,johoelzl/lean,digama0/lean,UlrikBuchholtz/lean,c-cube/lean,sp3ctum/lean,soonhokong/lean,fpvandoorn/lean2,digama0/lean,dselsam/lean,avigad/lean,leodemoura/lean,fpvandoorn/lean,soonhokong/lean-osx,digama0/lean,eigengrau/lean,dselsam/lean,leanprover/lean,rlewis1988/lean