Restrict Content Pro - REST API 1.2.2

Added new updater.

Fix: Check if endpoint class exists before instantiating. This protects against some rare "class doesn't exist" fatal errors

New: Add endpoints for renewing and cancelling memberships. Example: /wp-json/rcp/v1/memberships/{id}/renew and /wp-json/rcp/v1/memberships/{id}/cancel
New: Add support for retrieving customer by email or username.
New: Add has_trialed to customer endpoint argument whitelist. This allows you to update customers' has_trialed flag.
Refactor: Use lowercase id instead of ID. This is fully backwards compatible, so ID is still accepted and then converted.
Refactor: Use WP_REST_Server method constants when registering endpoints instead of hard-coded strings.
Refactor: Use WP_REST_Request::get_param() where possible. This also fixes an issue with JSON request formats not working.
Fix: PHP notices when adding a new membership via deprecated members endpoint.
Tweak: Update plugin author name and URL.