Feature Request: create variables from .json / .strings

[LinusGeffarth]

A new feature I'd love to have in this library (which would take huge efforts, I believe, though) would be to integrate the feature that Laurine has.

Ported over, it would look something like this:

lang-en.json

{
    "login": {
        "welcome": "Hey %, what's up?"
        "username": "Username",
        "password": "Password"
    }
}

ViewController.swift

welcomeLabel.text  = Localize.login.welcome(value: "Andres") // Hey Andres, what's up?
usernameLabel.text = Localize.login.username

That'd be super awesome!