enable multiple features in analytic tokens

[lbendavid-cloudinary]

Pull request for @cloudinary/url-gen

What does this PR solve?

enable creating feature flags for more than one feature in a single call

Final checklist

• Implementation is aligned to Spec.
• Tests - Add proper tests to the added code.

[const-cloudinary]

Does it preserve the order how the features where invoked?
I can see from the code that you just add them in a constant order.
As you know order matters.
It can provide useful information, for example when order is wrong or not optimal.