* Added missing param tags to functions
* Added comments to `wc_get_attachment_image_attributes` and
`wc_prepare_attachment_for_js`
* Fixed return type value for functions where it says bool but the code
returns array
* Renamed boolean to bool
Changes:
- WC_Cart::coupons_enabled() to wc_is_coupons_enabled()
- WC_Cart::get_cart_url() to wc_get_cart_url()
- WC_Cart::get_checkout_url() to wc_get_checkout_url()
This methods can be used in any place, but WC_Cart() is present only on
the frontend.