* Move authorship from individual (JJJ) to business (JJJ)
* Add sponsor.php to add "Sponsor" link to plugin row-actions
* Update donate link, from PayPal to Stripe
* Update support links, for WordPress.org & GitHub
* Bump "Tested up to" to 5.8 if needed
* Increment asset & minor version numbers
* Random small non-code related improvements (whitespace, grammar, URLs...)

Fixes #11

This change is necessary because the WP_Signup_Query class follows the common pattern used by WordPress itself, which does have support for MySQL GROUP BY.

* Text domain needs to match WordPress.org plugin slug
* Sub directory should match parent directory
* Make sure admin area assets are loaded in Network admin

WP User Signups vs. WP Signups is confusing anyways, because what else is a sign-up? The fact that blogs are "sign-ups" too is just a WordPress quirk that does not necessarily need to be called out and made prominent by this plugin. So here we are, half-in and half-out, and I think it's probably still gonna be OK.

* Rename list table to "Signups"
* Fix cache priming
* Improve error messages

* Extend WP_DB_Table class
* Docs updates

This shouldn't affect functionality, as nothing else is hooked in this early.

What a silly little error.