Drop PHP 7.0 support

[pinepain]

Rationale:

• PHP 7.0 is soon to be EOL (http://php.net/supported-versions.php);
• I'd like to start using new features from new PHP versions;
• I don't have much time to support PHP versions I don't use and maintain BC for them;

As this extension is currently under development and it public API could not be considered as stable and that extension is not yet widely used, such action shouldn't have negative effect on it's users.

If you are using php-v8 extension and for some reason have to stick to PHP 7.0 - please, let me know in comments. If you are willing to upgrade and capable to do that, please, let me know too in comments.

This poll considered to be open for the next two weeks and then will be closed and new version will be released without PHP 7.0 support.