Feature request: Support custom namespace separator

[dcodrin]

Tried migrating over to this library from next-i18next as this one supports everything that we need out of the box, like dynamic namespaces, unfortunately we have thousands of keys that are in this format:

{
  "someValue:description": "The translation"
}

Because of our usage of : in the key names, none of our transaltions work. i18next supports a custom nsSeparator. Would it be possible to support something like this on next-translate? Or are there any other suggestions around this, aside from converting all of our keys. Thank you for this awesome library btw!

[aralroca]

@dcodus thanks for that suggestion. I noted to 1.1