HAL: refactoring slice-weekday

[RuffaloLavoisier]

Refactoring the code below used to abbreviate the date.

{
  char weekday3[4];
  weekday3[0] = wd[0];
  weekday3[1] = wd[1];
  weekday3[2] = wd[2];
  weekday3[3] = '\0';
}