Improve file diff logger

[ackintosh]

I have improved the following two points.

• Execution time.

Added the state to FileDiffLogger whether already been executed once.

• Added the command-line option and configuration

FileDiffLogger is disabled by default, but the following will be enabled.

phync --file-diff /path/to/file

<?php
// config.php
return array(
    'destinations' => array(
        'foo.example.com',
    ),
    'file_diff' => true, // It is false if it is omitted.
);

[yuya-takeyama]

Sorry for not responding for so long.

I don't think anyone uses it anymore, so I'm closing it.