Update readme and stubs
Add ReflectionFiber::getFiber()
Add isStarted() method to Fiber and ReflectionFiber
Split ReflectionFiber into two classes
Update stubs
Drop Continuation object
Separate Fiber::run() into two methods Allows for creating fibers without such deep nesting and adds ReflectionFiber::fromFiber().
Drop ReflectionFiber::getThis()
Add ReflectionFiber