Drop PHP 7.1 support

[pinepain]

This would be a BC-breaking change.

Rationale is that upcoming php-v8 abstraction library is under development and I want to utilize new PHP 7.2 features, notably, object typehint.

If you are using php-v8 extension and for some reason have to stick to PHP 7.1 - please, let me know in comments. If you are willing to upgrade and capable to do that, please, let me know too in comments.

As of writing, I don't have specific due date for such changes. I guess I will match when top PHP frameworks (Symphony, Laravel) and development tools (xdebug, phpunit, code sniffer, mess detector) and others will fully support PHP 7.2.

[pinepain]

PHP 7.1 support will be dropped in php-v8 >= 0.3.x releases. If anyone is actively depend on it, please let me know in a timed manner. 0.2.2 (the next release) or 0.2.3, if any, would likely to close 0.2.x release series.