We music fans live for that moment when a song comes from nowhere – through a radio, perhaps, or more likely through your computer speakers nowadays – grabs us and doesn’t let go. That was undoubtedly the case with “Fast Car,” the first single by singer-songwriter Tracy Chapman. The song – for the ten or so of you who might have missed it over the better part of 20 years – is an achingly bittersweet, first-person ballad about a woman planning to escape her impoverished, broken family only to fall into the same…