I would like to use [Sync](https://github.com/rustyio/sync) on-the-fly recompiling with Cowboy project assembled using relx (as per Cowboy [Getting Started Guide](http://ninenines.eu/docs/en/cowboy/HEAD/guide/getting_started/)).

The problem is that even if I manage to get Sync starting in my application by mentioning sync in applications list in my\_application.app.src file like this:

```
{application, my_application, [
    {description, "My Cowboy Application"},
    {vsn, "0.1.0"},
    {modules, []},
    {registered, [my_app_sup]},
    {applications, [
        kernel,
        stdlib,
        cowboy,
        sync
    ]},
    {mod, {my_app, []}},
    {env, []}
]}.`

```

I still can't get it working because of relx assembler does not move my source code to \_rel directory (of course, it shouldn't). 

Is there any way to tell Sync where my source files are located? Or may be I'm totally wrong and Sync integration with relx must be done in some other way?