Mercury Sable has been improved in all the key areas for 2000 - appearance, mechanicals and accommodations. The new Sable presents a pleasingly muscular look, validated by upgraded powertrains, increased responsiveness and surprisingly agile road manners.This bread-and-butter family sedan has one big trick up its sleeve--it's a pleasurable drive for even the most enthusiastic driver. And its agility doubles as an important adjunct to its comprehensive inventory of safety features. The interior spaces are spacious and pleasing, and by and large, its controls and instrumentation are contemporary, straightforward and easy to use. As