feat(util/sexpr/option_declarations): add register_string_option
feat(util/sexpr/option_declarations): add register_string_option

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