Switch assert_options(ASSERT_ACTIVE) to ini_get("zend.assertions") ==…

…= "1"

Merge pull request #2 from steven-hoffman-jomashop/php-81-supress-jso…

…nserialize-return-type

Prevents a warning in PHP 8.1 - BN class uses ReturnTypeWillChange attribute on jsonSerialize

fixing assert with string (php 7.2 deprecated)

Composer.json fix

Migration from raw gmp to simplito/bigint-wrapper-php