CAR's Mazda MX-5 roadster is such a joy to drive, even in the creeping clutch of winter. It feels so alert, so tail-up and feisty – an engaging effervescence that makes every mile something to be enjoyed, no matter what the road or the weather.Still fresh and still relevant 20 years after the launch of the original, the MX-5 has adhered tenaciously to its straightforward but hugely effective