Tweak: API Status requests are now uniquely cached, with individual expire times, if the Instance ID is sent in the request.
Tweak: Auto log SmartCache errors.
Add: Added log_error() method to WC_AM_Log() class.
Add: Added log_info() method to WC_AM_Log() class.
* Fix: URL expire time for local downloads was calculated incorrectly.
* Fix: Array to string conversion notice in SmartCache.
* Tweak: Set WooCommerce_API_Manager class variables to private. Variable values accessible with getters.
* Constants added:
- WC_AM_VERSION
- WC_AM_WC_MIN_REQUIRED_VERSION
- WC_AM_REQUIRED_PHP_VERSION
- WC_AM_WC_SUBS_MIN_REQUIRED_VERSION
* Fix: When more than one WooCommerce Subscription product was purchased in an order, only one API Resource was created for one WooCommerce Subscription product, rather than one API Resource for each WooCommerce Subscription product
