Multirun support for ibazel_notify_changes

[pauldraper]

I'd love to have support for bazel-watcher's ibazel_notify_changes.

Basically, ibazel watches for changes and restart executables. But it doesn't restart executables with the ibazel_notify_changes tag (e.g. a live reload web server), rather it writes events to stdin to notify them.

The multirun would need to be a ibazel_notify_changes executable and understand which of its children should be restarted vs be passed build events on stdin.

[ash2k]

I've never used ibazel myself. Contributions are welcome!