Threaded implementation of NodeBase

[auriium]

Title. We only need this to compete with other frameworks. This will probably introduce a Beetle dependency.

[A248]

Are you sure you want Branch to depend on Beetle? From the perspective of each library's relative position in the dependency stack, I would not expect a mid-level/high-level library like Branch to depend on a very high-level library such as Beetle.

[auriium]

Hmm, you're right. However, the reason for the dependency would only be for something like CustomFutures from Beetle. I could easily do away with the beetle dependency by making the API use CompletionStage implementations like CompletableFuture instead.