[core.lib] Add basic "pretty" printing to `store_conf'.

The format is as follows:

```
{
  table = {
     foo = 1,
     bar =2,
  }
  array = {
    1,
    2,
  }
}
```

Its not *really* pretty, but somewhat readable and the algorithm is simple. Idiomatic Lua formatting would be much more complicated as far as I can imagine.