Support for named tokens for format string

[cleverguy25]

What is the appetite for supporting named tokens in a new method, to be called like this:

en:{
    welcome:"welcome |firstName|, your status is |Status|."
  }
  ...
  var tokens = { firstName: "John", status: "Accepted" };
  strings.formatStringWithTokens(strings.welcome, tokens);

The benefit of this is that when the strings are handed over to localization teams they have more context of the value in those fields and less room for error.

[joshsalverda]

I also needed this, so modified the code to support it: https://github.com/stefalda/react-localization/pull/59

[clytras]

@joshsalverda the PR is merged, so I think this should be closed.