Add support to quoted keys

Mm I found a little problem along the way:
both toml and json should support keys like:
toml
```toml
site."google.com" = true
```
json
```json
  "site": {
    "google.com": true
  }
```

But onion doesn't, it split it in `site, google, com` instead of `site, "google.com"`
Should we support this?