[Suggestion] Add support for nested objects about frenchkiss.js

[vthibault]

The main reasons we didn't add support for nested objects are the following :

• What happened if we ask in your example t('fruits') ? Handled by onMissingKey() ?
• What happened if we currently have a key named "fruits.apple" in the table ? Which one should have priority, the key or the nested resolution ?
• Need some checks to avoid TypeError t('fruits.undefinedKey.typeerror') or object escaping t('fruits.constructor.constructor.name') === 'Function'
• Need to implement nested support in extends function.
• To keep the implementation fast and avoid re-parsing the key at each call, we need to store the generated function in an inline cache object (cache['fruits.apple'] = <generated function>) leading to problems while updating the table, deleting parent of nested entries or erasing the parent with a string.

For this reason, and because I don't really get the point of nested objects except developers comfort, we didn't feel the need to implement it in the first version.

But still, it's on the roadmap, even if I'm not sure about the first two questions.