WooCommerce Customer Order XML Export Suite 2.6.3

* Fix - Export filenames in Export List were not properly escaped, which made it possibly vulnerable to a stored XSS exploit
* Fix - PHP notices when export data isn't found or file isn't writeable
* Fix - Duplicated fields for custom meta in customer exports are removed
* Fix - Ensure invalid characters can't be used for a field name

* Feature - Export customers directly from the "Users" list via bulk action
* Feature - Add static values (such as shop name) to custom export formats
* Feature - View exported XML in a new browser tab without downloading export file
* Tweak - Use direct SQL queries for background jobs to prevent caching issues on certain hosts
* Tweak - Use GET request to dispatch background jobs as a workaround to POST request rate-limiting issues on certain hosts
* Dev - Add array keys to export options for easier customization

* Fix - Orders could exported multiple times when auto-export schedule was "immediately"
* Fix - Require user to be logged in to download exported files