[spacemacs-defaults] Tweak savehist configuration

[fnussbaum]

1. Use an idle timer instead of a strict periodic autosave interval. Saving large histories can cause noticable delays, and the default history-length set by Spacemacs is relatively large (1000).

2. Save kill-ring without text properties, as they are known to cause significant performance problems and huge history files in some cases, and persisting them in the kill-ring usually brings little benefit. This should fix Spacemacs freezes from time to time. When this happens it eats up almost all memory and CPU. #1300, fix Spacemacs gets stuck for a few seconds and hogs CPU(100% usage) from time to time #1369 and fix emacs eats cpu 100% frequently #9409 again.

3. Add kmacro-ring and log-edit-comment-ring as additional variables. They are useful and usually not very large. BTW, search-ring, regexp-search-ring and extended-command-history are redundant here as long as long as savehist-save-minibuffer-history is non-nil (the default). I decided to leave them there for now to avoid any breaking changes for users that customized that option, though I guess it could be okay to change this.

[fnussbaum]

1. Use an idle timer instead of a strict periodic autosave interval. Saving large histories can cause noticable delays, and the default history-length set by Spacemacs is relatively large (1000).

I think an idle timer is a reasonable choice here, note that savehist-autosave is also called in the kill-emacs-hook. So the only case where this change would cause more savehist data to be lost than before is if users work for a long time without ever pausing for a minute, and then Emacs crashes in a way that does not trigger kill-emacs-hook (which should be very rare). But let me know if you object to this.

[smile13241324]

This looks very good