Add a symbol property to get current option chain's option

Now it's not possible to access option chains' current opts outside the chain callback, what if we can access the current opts of the option chain with a predefined symbol?

```js
optionChain.optsSymbol = Symbol('option-chain-opts')
```

```js
const fn = optionChain(optionDefinition, printOptionsAndArgs);
fn.foo[optionChain.optsSymbol] //=> {foo: true};
```
