Support for Lazy<T> like Dagger

I've implemented a version of [Dagger's `Lazy`](https://github.com/square/dagger/blob/master/core/src/main/java/dagger/Lazy.java) in [Sangria](https://github.com/tavianator/sangria/blob/master/sangria-lazy/src/main/java/com/tavianator/sangria/lazy/Lazy.java). But it's somewhat limited; `Lazy` works automatically but `@Annotated Lazy` requires you to explicitly add a binding. That's about as good as an extension can do. There are some alternatives:
1. Have Guice support its own `Lazy` out of the box, in a similar way to how `Provider` injection works now.
2. Have Guice expose some kind of support for "pluggable bindings." Then I could write something like `bind(new LazyKeyMatcher()).to(new LazyGuicePlugin())` and the plugin would generate bindings on the fly.

Is there any interest in doing something like 2? If so I can code up a proof of concept.