weekday – Generate "day of week"

Macros \week­day{yyyy}{mm}{dd} (yields day name) and \week­day­date{yyyy}{mm}{dd} (yields date print-out, in­clud­ing day name). You may use \year, \month, \day, to gen­er­ate to­day's day name.
The code bears a note about year 2000 com­pat­i­bil­ity; it is not clear whether it will be work­able in our present post-mil­len­nial state.