Secret callback about baseplate.go

[fishy]

I like the channel idea. Just two things to note:

1. We shouldn't change NewStore because most of the use cases doesn't need the callback. We can create a new one like NewStoreWithCallback
2. The notify <- secrets should probably be in its own goroutine, otherwise if the caller didn't read from the channel timely, this would block the parser.

[konradreiche]

What does a downstream client mean? Is that a client implementation you are providing yourself outside of baseplate.go?

[fishy]

What does a downstream client mean? Is that a client implementation you are providing yourself outside of baseplate.go?

Yes.

[andizzle]

This is addressed by #20

[fishy]

We still need to allow registering of middlewares after initialization, but that can be in its own ticket.