feat(emacs/lean-mode): add lean-tab-indent-or-complete
feat(emacs/lean-mode): add lean-tab-indent-or-complete

Close #105

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