Update with @stacks.js/* and various minor improvements

[markmhendrickson]

• Integrate @stacks/auth instead of @blockstack/connect
• Reduce Stacks-related code duplication with new stacks module
• Improve README with new screenshot
• Normalize naming around "Todos" instead of "To-do list" etc.
• Broaden scope of homepage tagline
• Simplify package name and add author
• Fix minor React-related console warnings

This PR resolves / supplants #53 and is needed mainly to update content found at https://docs.blockstack.org/authentication/building-todo-app to see how Stacks.js is used to integrate authentication.

[yknl]

LGTM

[markmhendrickson]

@kyranjamie Mind reviewing again with particular focus on the stacks.js module? I've refactored more of the @stacks/* imports into it so that we can reference them all in one place from the docs and keep things simpler for readers.

[kyranjamie]

I can, though following discussion here, maybe we want to wait before merging this if we're going to change the packaging structures so that connect exports auth, rather than this way around.

[markmhendrickson]

I'd prefer not to make that packages discussion blocking here since the related documentation is currently broken and need these changes urgently to fix them.

[kyranjamie]

LGTM @markmhx

I'd be inclined to rename src/stacks.js to stacks-auth or something to be a bit more descriptive what it contains, otherwise looks clean.

[markmhendrickson]

@kyranjamie I've improved the relevant src libraries into auth.js and storage.js. Mind taking another look?

[kyranjamie]

All good