minor, precompute values for format specifiers for __strfdtdur() beforehand

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'core/calc-as-needed'

* core/calc-as-needed:
  minor, precompute values for format specifiers for __strfdtdur() beforehand
bump, release v0.2.7 is imminent

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>