Is it possible to ensure streams a actually scheduled by the time the call returns?

[couling]

Similar to #20 but subtly different. I'm having trouble with a race condition formed of the following:

Main thread:

• Creates Observer
• adds Stream
• starts Observer thread
• modifies a file

Observer thread:

• Registers cache of streams with native library
• enter's native library's loop

Expected behaviour here might be for the observer to always be notified of the file modification. The stream is registered on the main thread before the file is modified. But because that will be cached in the python object and only registered with the OS library on a separate thread, the OS native library might not be informed of the stream until after it was modified.

It would be great if all schedule events could be in place by the time the .schedule method completes.