minor, provide YMCW like dates for echs_every_month() builder too

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
fix, properly check if echs_every_*() events with ymcw dates are before or after the initial instant

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, provide simple echs_bday_{after,before}{,_or_on}() builders for business day moving

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'feat/builders' into next

* feat/builders:
  minor, provide simple echs_bday_{after,before}{,_or_on}() builders for business day moving
  fix, properly check if echs_every_*() events with ymcw dates are before or after the initial instant
  minor, provide YMCW like dates for echs_every_month() builder too
Merge branch 'next'

* next:
  minor, provide simple echs_bday_{after,before}{,_or_on}() builders for business day moving
  fix, properly check if echs_every_*() events with ymcw dates are before or after the initial instant
  minor, provide YMCW like dates for echs_every_month() builder too
  minor, adapt uk holiday list to use ymcw-dates directly
  minor, support YMCW like dates for echs_every_year()
  hygiene, declare mdays[] private array globally in builders.c
  Revert "major, introduce slots for ymcw dates in union echs_instant_u"
  minor, introduce ymcw opers FIRST/SECOND/...
  major, introduce slots for ymcw dates in union echs_instant_u