`syncedFetch` is a simple wrapper around `fetch` to reduce boilerplate.

- `get`: The URL to get. If it is an observable or Selector function, it will re-run whenever the value changes.
- `set`: The URL to set
- `getInit`: The `init` parameter to pass to `fetch` when getting
- `setInit`: The `init` parameter to pass to `fetch` when setting. Defaults to `{ method: 'POST' }`
- `valueType`: The function to call on the Response set. Defaults to `json`.
- `onSavedValueType`: The function to call on the Response from set. Defaults to the `valueType` option or `json`.
- `onSaved`: Given the return value from set, return a value to save back into the observable.

Example:

```ts
import { syncedFetch } from '@legendapp/state/sync-plugins/fetch';
import { observable } from '@legendapp/state';

const state$ = observable(syncedFetch({
    get: 'https://url.to.get',
    set: 'https://url.to.set',
    onSaved: (value) => {
        return {
            updatedAt: value.updatedAt
        }
    }
}))
```