add FileCacheManager

Add support for caching information about state of fixing files.
Cache is supported only for phar version and version installed via composer.
 
 File will be processed by PHP CS Fixer only if any of the following conditions is fulfilled:
 * cache is not available,
 * fixer version changed,
 * file is new,
 * file changed.
One can run php-cs-fixer from any location and set whatever dir he wants.
In case you presented there will be `src/.php_cs.cache` and `spec/.php_cs.cache`, all with paths relative to it's dir, so 'foo.php', not 'src/foo.php'