* Updated compatibility with WooCommerce 3.4.
* Fixed plugin version constant.
* Updated plugin links.
* Added the Woo plugin header tag.
* Added ABSPATH checks.
* Fixed some minor issues in the internal API documentation.
* Replaced use of language domain constant with string literal.
* Updated compatibility with WooCommerce 3.3.
* Updated compatibility with WordPress 4.9.
* Updated access to product, documentation and support resources.