date: make it accept ISO date format. Fix help text.

make testsuite actually test something useful.

function                                             old     new   delta
date_main                                           1094    1149     +55

include/usage.h

@@ -612,8 +612,9 @@
 	) \
      "\n" \
      "\nRecognized formats for TIME:" \
-     "\n	[hh:]mm:ss" \
+     "\n	hh:mm[:ss]" \
      "\n	[YYYY.]MM.DD-hh:mm[:ss]" \
+     "\n	YYYY-MM-DD hh:mm[:ss]" \
      "\n	MMDDhhmm[[YY]YY][.ss]" \
 
 #define date_example_usage \