Enable forward-history-search in zsh with ^S

I use `^R` a lot in the shell to backward search my history for a command, as I'm sure a lot of developers do. But I usually go so fast that I often pass the one that want. In Bash, you can run `^S` to forward search, but you have to disable terminal flow for it work properly. This would be neat to be in zsh too.

Turning off XON/XOFF flow control allows for forward history searching to work, so that now if I'm using `^R` to search my history for a command, if I pass it, I can run `^S` right away to search get back to that command seamlessly.

What are your thoughts here? Does anyone else feel this would be useful?