Allow rotating between regex builders

[glucas]

As requested here: https://emacs.stackexchange.com/questions/33921/how-to-switch-between-ivy-completion-styles

It might be useful if ivy-hydra's built-in C-o m command to toggle the re builder could also be used to switch to the ivy--regex-ignore-order builder -- or more generally to rotate between a customizable list of re builders.

[abo-abo]

Thanks, this would be useful to add. PR welcome.