[calendar] very_short_weekdays fallback to datatype-date-format langage data

Both shortWeekDays and weekDays will be localized at least datatype-date-format
is available in specified language. Fix #1796.
[calendar] Tweak the indent
[io] Add documentation for Y.io and IO.send return values
Merge remote-tracking branch 'origin/live-docs' into dev-master
Merge branch 'fix1796' into dev-master
[calendar] Update HISTORY
[calendar] Build