Support quoted keys in logger config

If we configure loggers like this:

```conf
logger {
  a.b = WARN
  a.b.c = DEBUG
}
```

`a.b` as a string is lost because it becomes an object in `a.b.c`. To get around this we can quote the keys:

```conf
logger {
  "a.b" = WARN
  "a.b.c" = DEBUG
}
```

This PR adds support for quoted keys in the logger config, by parsing the config path and then rejoining it. Supports quoting anywhere within the path, like `x."y.z"`.
What have you got against retro?