feat(library/data/list/basic): define 'union' and 'insert' for lists
feat(library/data/list/basic): define 'union' and 'insert' for lists

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