Hooks to include error in return instead of throw errors

Currently if client isn't ready hooks will throw an error. 

I think it would be much nicer if it simply returned an error like useSWR does.

return 
```ts
const value: {
  decision: OptimizelyDecision | null,
  clientReady: boolean,
  didTimeout: boolean,
  isLoading: boolean,
  error: Error | null
}
```