Setup layout to include functions separated for posts and cron

[marcoarthur]

We should write under inc/functions (path) the separate concerns about posts functions (retrieval of posts with the given parameter id from a child) and the functions related to setup cron task. And require those modules from the plugin entry under Wp-sync.php. Another alternative is to put inc/main.php and create an wp_sync_init() function. So we can load all required modules