[feature] be able to pause node

[gabrielcsapo]

I am currently working on a tool that helps understand what is happening in a broccoli build. (gabrielcsapo/broccoli-inspector#5) One of the features that I am working on is making it easier to introspect into the build process by being able to pause a node and enter a debugging session.

It would be great if this was possible;

watcher.builder.on('beginNode', (node) => {
  node.pause();
  // start chrome debugging session that will eventually be able to call node.continue()
});