[WIP] Release: v2.0.0 - Hooks based API

# Context

This library is already almost 2 years old. There is a lot of people who come to this as an easy way out to set up firebase authentication in react applications since it aims to be very straightforward, and I'd say it achieves the goal well.

Yet, I'm not completely happy with the current Higher Order Function design, and I feel like the current API offering static implementations of authentication methods creates a sort of vendor lock-in to this library, which I don't appreciate and feel like we could offer something more flexible instead.

# Proposal

First: a Hooks based API.

Most folks that come to use this library want to just have it managing the state regarding firebase authentication and ease to just hook `firebase.auth()` into a component and have methods ready to go.

The very same experience could be given through a `useFirebaseAuth()` hook.

_(more details to come)_

The proposal names a future useFirebaseAuth() hook and the existing firebase.auth() integration, but provides no files or tests. Start by reading the current higher-order component API and authentication state handling. The work is done when the hooks-based API is specified and implemented with behavior equivalent to the existing authentication flow.

Written by the indexing model from the issue text.