Flysystem plugin system implementation with tags

Hi,

thank you for your work, it was a pleasure to enter in your source code.
I add the plugin implementation of plugin flysystem.

Regards,
[Coding Style](http://www.php-fig.org/psr/psr-2/)

> Opening braces for methods MUST go on the next line, and closing braces MUST go on the next line after the body.