Features: add new functionis to retrieve and manipulate notifications

Hi,

Not sure if you'd be interested, but I've recently made new functions to support retrieve the "toast" object from a "toaster service" user perspective.
My use case is that I want to show a sticky notification message when the user triggers a long server request and when it completes, update the message inside the same notification message.

Example:
As a user, 
When I do a search for thousands of records.
Then I see a notification message telling me it's started (info)
And after 30s, I see that the same notification message turned green and says it's done (success).

I know I could show individual notification messages for each step but I wanted to avoid having a stack growing up; and also to keep the notification message visible as long as the operation is running.

There's also a few other changes: 

1. README text additions
2. Some side-bugs I found like some problems with clearing timeouts

You don't have to merge this, I'm just letting you know what I'm doing with your library.

Cheers,

David