Added option to split key via different symbol

This is my attempt to add the option to not split keys when there is a '.' in the lookup name. 

The following locale file:
```js
{
  'dont.split.on.dots': 'hello'
}
```

When calling translate with `splitkeyChar` option set to anything but a `.` yields:

```js
translate('dont.split.on.dots', { splitKeyChar: '*' });  // => 'hello'
```