QDate: add conversions for std::chrono calendaring classes

std::chrono::year_month_day and related classes offer very
convenient to specify dates.

This patch adds implicit constructors to QDate to support this
convenience, e.g.:

  // YYYY-MM-DD, DD-MM-YYYY, MM-DD-YYYY formats:
  QDate d1 = 1985y / December / 8;
  QDate d2 = 8d / December / 1985;
  QDate d3 = December / 8d / 1985;

  // Indexed weekday:
  QDate d4 = 2000y / January / Monday[0];
  QDate d5 = 2000y / January / Monday[last];

and so on.

These are all implemented using the conversion from the std
calendaring classes to sys_days. Conversions between sys_days
and QDate are also added, since they're basically "for free".

I don't expect "ordinary" users to stumble upon it, but it's
worthy mentioning that std::chrono::year *does* have a year
zero (hence, year_month_day in year 0 or below are offset
by one with the corresponding QDate). I've left a note
in the documentation.

[ChangeLog][QtCore][QDate] QDate (and therefore QDateTime)
is now constructible using the year/month/day/week classes
available in the std::chrono library. Moreover, it now
features conversions from and to std::chrono::sys_days.

Change-Id: I2a4f56423ac7d1469541cbb6a278a65b48878b4a
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

0 files changed, 0 insertions, 0 deletions