Simplify submitting commands using lambdas or method references #23

We currently have a method to submit a command for execution:

Strongback.submit(Command)

While this works, we should add overloaded methods that take:

• a Runnable function that executes one time;
• a Runnable function that executes one time, a time to pause, and another function that is called after the pause time;
• a BooleanSupplier that executes repeatedly while the function returns true;
• a BooleanSupplier that executes repeatedly while the function returns true, and a maximum duration that the command should run