Merge branch 'next'

* next: (23 commits)
  fix, PEBKAC, it's toy1.mmy.series for series-over-mmy reader regressions
  test, provide regression tests for series reader through mmy API
  minor, adapt to the fact that trym's carry numeric months in truffle.c
  minor, switch read_series() (et al) to using read_trym() from the mmy API
  minor, provide some idate helpers (getters for y, m, and d slots)
  chore, define and use TRYM_ABS_CUTOFF in code using the mmy API
  minor, switch to using mmy API in trod.c
  chore, remove unused __p2c() code
  minor, use literal TRYM_YR_CUTOFF instead of hard-coding it
  minor, change signature of read_trym()
  chore, compile libtruffle with mmy.c code
  minor, provide read_trym() in mmy.c
  minor, provide means to convert between relative and absolute trym_t objects, ...
  chore, switch to using cym_to_trym() in truffle code
  chore, switch to using cym_to_trym() in series code
  hygiene, cons slot of struct trtsc_s is actually a trym_t*
  minor, define trym_t in mmy.h
  minor, flip truffle over to handling series through libtruffle
  fix, hygiene, define DECLF and DEFUN in dt-strpf.h
  minor, build libtruffle with series support
  ...