* Feature - Manage the Mailchimp newsletter subscription from the "My Account" page.
* Tweak - MailPoet 2 provider has been marked as deprecated.
* Tweak - Added link to get support in the plugin list.
* Tweak - Open the documentation link in a new tab.
* Tweak - Tested compatibility with WP 6.3.
* Dev - Dropped deprecated plugin code on versions 3.x.
* Dev - Dropped `Campaign Monitor` API client.
* Dev - Dropped deprecated filter hook `wc_newsletter_subscription_checkout_content_location`.
* Dev - Dropped deprecated filter hook `woocommerce_newsletter_mailchimp_api_request`.
* Dev - Updated the minimum requirements to WC 3.7, WP 4.9, and PHP 5.6.
