chore(library/blast/state): document branch extension methods
chore(library/blast/state): document branch extension methods

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