feat(library/data/option): add `monad` instance
feat(library/data/option): add `monad` instance

soonhokong/lean-osx,fgdorais/lean,Kha/lean,johoelzl/lean,digama0/lean,digama0/lean,rlewis1988/lean,leanprover/lean,soonhokong/lean-osx,leanprover/lean,fgdorais/lean,leanprover/lean,rlewis1988/lean,Kha/lean,rlewis1988/lean,dselsam/lean,leanprover/lean,leanprover-community/lean,avigad/lean,fpvandoorn/lean,avigad/lean,Kha/lean,fgdorais/lean,digama0/lean,Kha/lean,leodemoura/lean,fpvandoorn/lean,avigad/lean,leodemoura/lean,fpvandoorn/lean,leanprover-community/lean,leodemoura/lean,leanprover/lean,soonhokong/lean-osx,dselsam/lean,avigad/lean,fgdorais/lean,leodemoura/lean,soonhokong/lean-windows,leanprover/lean,leodemoura/lean,rlewis1988/lean,soonhokong/lean-windows,avigad/lean,leanprover-community/lean,digama0/lean,avigad/lean,rlewis1988/lean,digama0/lean,dselsam/lean,fpvandoorn/lean,johoelzl/lean,soonhokong/lean-windows,dselsam/lean,fgdorais/lean,johoelzl/lean,leodemoura/lean,digama0/lean,johoelzl/lean,leanprover-community/lean,leanprover-community/lean,leanprover-community/lean,rlewis1988/lean,dselsam/lean,Kha/lean,soonhokong/lean-osx,fgdorais/lean,soonhokong/lean-windows,johoelzl/lean,soonhokong/lean-osx,fpvandoorn/lean,dselsam/lean,fpvandoorn/lean,soonhokong/lean-windows,johoelzl/lean,Kha/lean