[wishlist item] Export/Import customized item.

Here's a wishlist item for whoever is keeping track of them to tuck away for us... I'd like to be able to run a `M-x export-customized-item' command, sending output to a file, the current buffer, an arbitrary buffer, a variable, (or network socket?), then on my laptop run `M-x import-customized-item' in order to transfer settings from one to the other. The import function ought to be smart enough to merge face specs, possibly prompting for precedence and/or overrides. It should be able to join lists, such as `savehist-history-variables', `After-save-alist', or the `scheme-lock' keyword lists.