fix, PEBKAC, construct ywd from daisy through __make_ywd_c() ctor
test, fix, PEBKAC, adapt dseq.25.clit to correct values
fix of fix, daisy already provides week counts based on Mondays
Revert "fix, PEBKAC, construct ywd from daisy through __make_ywd_c() ctor"

This reverts commit a5bc2420cece89a285c387f281a0ef3ea77f1db7.
fix, assing to ywd directly (including hang slot)

The reason is that the daisy type already has all the data
needed for a correct ywd calculation.  No need to calc things
twice.
hygiene, attribeautify yd routines as const and pure
minor, provide routine to derive jan-01'th weekday from day-of-year and its weekday
hygiene, factor canonicalisation of iso weeks out into canon_yc() macro
fix, actually compute the correct jan-01 weekday in __get_jan01_yday_dow()
provide __make_ywd_yd_dow() to obtain an ISO-8601 ywd from the year, day-of-year and its weekday
minor, express __daisy_to_ywd() in terms of __make_ywd_yd_dow()
hygiene, eradicate __get_cumwk()
hygiene, attribeautify daisy routines as const and pure
Merge branch 'core/ywd'

* core/ywd:
  hygiene, attribeautify daisy routines as const and pure
  hygiene, eradicate __get_cumwk()
  minor, express __daisy_to_ywd() in terms of __make_ywd_yd_dow()
  provide __make_ywd_yd_dow() to obtain an ISO-8601 ywd from the year, day-of-year and its weekday
  fix, actually compute the correct jan-01 weekday in __get_jan01_yday_dow()
  hygiene, factor canonicalisation of iso weeks out into canon_yc() macro
  minor, provide routine to derive jan-01'th weekday from day-of-year and its weekday
  hygiene, attribeautify yd routines as const and pure
  fix, assing to ywd directly (including hang slot)
  Revert "fix, PEBKAC, construct ywd from daisy through __make_ywd_c() ctor"
  fix of fix, daisy already provides week counts based on Mondays
  test, fix, PEBKAC, adapt dseq.25.clit to correct values
  fix, PEBKAC, construct ywd from daisy through __make_ywd_c() ctor