Tiny Singapore had embraced electric scooters in a big way, but deaths and fires linked to the two-wheelers have prompted authorities to introduce tough rules that could put a brake on their runaway success.The contraptions have popped up in cities worldwide but pedestrians in many places have come to see the silent machines as menaces, and authorities have been scrambling to regulate them.Tens of thousands flooded Singapore, becoming particularly popular among commuters and workers deliverin