Move command execution into its own task
De-duplicate events

Some text editors produce multiple file system events when they save a
file. Zwobot handles this by delaying command execution by 50ms and
canceling the execution if another one follows within that time.
Fix placement of command markers
Print output as it comes in
Refactor
Run command once before starting event loop

My use case for Zwobot is to run a continuous testing loop that triggers
whenever my code changes. When I start this loop, I usually want the
first test run right away.
Add stdout/stderr prefixes to output