Fluent-Ergonomics

This is a short-term wrapper around the Fluent-RS library. The Fluent-RS maintainers acknowledge that the core has little in the way of ergonomics, and they have two different libraries that they are developing to provide those. No ergonomics library is mature at this time, and this one follows just my own pattens of use which may not be suitable for all users.

I do expect to deprecate this eventually.

lib.rs:

Provide a more ergonomic interface to the base Fluent library

The Fluent class makes it easier to load translation bundles with language fallbacks and to go through the most common steps of translating a message.