Stdlib\Options: Misc enhancements 

* Minor performance tweak - consolidate calls to method_exists
* Replace method_exists with more reliable is_callable
* CS fixes
ZF2 normally uses `sprintf()` for exception messages.

```php
throw new Exception\BadMethodCallException(sprintf(
    'The option "%s" does not  have a callable '
    . '"%s" setter method which must be defined',
    $key,
    $setter
));
```