Enhancement: Allow settings changes via WP-CLI

[rklrkl]

When you host many WP sites, WP-CLI becomes incredibly useful to change multiple WP sites on an automated basis. At the moment, Simple History just has a "list" option for WP-CLI (bet you didn't even know it had that - no mention of it is made on the wordpress.org page for the plugin!).

I would ultimately like all the settings options in Simple History to be controllable via WP-CLI (and further added to in the future if a new option is added). This would dramatically improve Simple History for Web hosters, IMHO.