* Port for php8
* Port php c extension for php8
* Update composer.json
* Drop php7.0 support
* Update phpunit for php7.1 in c extension test
* Add back support for php7.0
* Add badge for php8 continuous build
* Only ported c extension to php8.
* Didn't fixed the issue of throwing warnings for missing arginfo in bundled files.
* Tests not fixed, because syntax of phpunit (<7 vs >9.3) are not compatible.
* In next release, needs to drop php5 and php7.0 support (in order to use phpunit > 7)
