add t_start, t_end and visibility_changed to docs
add t_start, t_end and visibility_changed to docs

sdgdsffdsfff/boomerang,levexis/boomerang,yahoo/boomerang,lognormal/boomerang,FredXue/boomerang,forcedotcom/kylie,levexis/boomerang,sdgdsffdsfff/boomerang,FredXue/boomerang,forcedotcom/kylie,lognormal/boomerang