Rename day_point to sys_days

Boost-datetime-Examples-Translated.md

@@ -110,7 +110,7 @@ look if ported to this library.
             auto d = year(y)/m/day;
             if (!d.ok())
                 throw std::exception{};
-            auto birthday = day_point(d);
+            auto birthday = sys_days(d);
             auto today = floor<days>(current_zone()
                                        ->to_local(system_clock::now()).first);
             auto days_alive = today - birthday;
@@ -143,11 +143,11 @@ look if ported to this library.
         auto today = floor<days>(current_zone()->
                                    to_local(system_clock::now()).first);
         auto current_year = year_month_day{today}.year();
-        auto days_since_year_start = today - day_point(current_year/jan/1);
+        auto days_since_year_start = today - sys_days(current_year/jan/1);
         std::cout << "Days since Jan 1: "
                   << days_since_year_start.count() << '\n';
         auto days_until_year_start =
-            day_point((current_year + years{1})/jan/1) - today;
+            sys_days((current_year + years{1})/jan/1) - today;
         std::cout << "Days until next Jan 1: "
                   << days_until_year_start.count() << '\n';
     }
@@ -262,11 +262,11 @@ look if ported to this library.
     #include <iostream>
     #include <vector>
 
-    std::vector<date::day_point>
+    std::vector<date:: sys_days>
     generate_holidays(date::year y)
     {
         using namespace date;
-        std::vector<day_point> holidays;
+        std::vector< sys_days> holidays;
         holidays.push_back(y/jan/1);       // Western New Year
         holidays.push_back(y/jul/4);       // US Independence Day
         holidays.push_back(y/dec/25);      // Christmas day
@@ -362,7 +362,7 @@ look if ported to this library.
         using namespace std::chrono;
         using namespace date;
 
-        auto d = day_point(2002_y/feb/1);  // an arbitrary date;
+        auto d = sys_days(2002_y/feb/1);  // an arbitrary date;
         // construct a time by adding up some durations durations
         auto t1 = d + 5h + 4min + 2s + 1ms;
         // construct a new time by subtracting some times
@@ -411,7 +411,7 @@ look if ported to this library.
         using namespace std::chrono;
         using namespace date;
         auto zone = current_zone();
-        auto t10 = day_point(2002_y/jan/1) + 7h;
+        auto t10 = sys_days(2002_y/jan/1) + 7h;
         auto t11 = zone->to_local(t10);
         std::cout << "UTC <--> Zone base on current setting\n";
         std::cout << t11.first << ' ' << t11.second << " is "
@@ -422,7 +422,7 @@ look if ported to this library.
         // eastern timezone is utc-5
         zone = locate_zone("America/New_York");
         // 5 hours b/f midnight NY time
-        auto t1 = day_point(2001_y/dec/31) + 19h + 0s;
+        auto t1 = sys_days(2001_y/dec/31) + 19h + 0s;
         std::cout << "\nUTC <--> New York while DST is NOT active (5 hours)\n";
         auto t2 = zone->to_sys(t1);
         std::cout << t1 << " in New York is " << t2 << " UTC time\n";
@@ -431,7 +431,7 @@ look if ported to this library.
         std::cout << t2 << " UTC is " << t3 << " New York time\n\n";
 
         // 4 hours b/f midnight NY time
-        auto t4 = day_point(2002_y/may/31) + 20h + 0s;
+        auto t4 = sys_days(2002_y/may/31) + 20h + 0s;
         std::cout << "UTC <--> New York while DST is active (4 hours)\n";
         auto t5 = zone->to_sys(t4);
         std::cout << t4 << " in New York is " << t5 << " UTC time\n";
@@ -441,7 +441,7 @@ look if ported to this library.
 
         // Arizona timezone is utc-7 with no dst
         zone = locate_zone("America/Phoenix");
-        auto t7 = day_point(2002_y/may/31) + 17h + 0s;
+        auto t7 = sys_days(2002_y/may/31) + 17h + 0s;
         std::cout << "UTC <--> Arizona (7 hours)\n";
         auto t8 = zone->to_sys(t7);
         std::cout << t7 << " in Arizona is " << t8 << " UTC time\n";
@@ -458,7 +458,7 @@ look if ported to this library.
     {
         using namespace std::chrono;
         using namespace date;
-        auto d = day_point(2002_y/feb/1);  // an arbitrary date
+        auto d = sys_days(2002_y/feb/1);  // an arbitrary date
         auto t = d + 3h + 5s;              //an arbitray time on that day
         if (d <= t && t < d + days{1})
             std::cout << d << " contains " << t << '\n';
@@ -514,7 +514,7 @@ an example using the IANA timezone database see the [Local to UTC Conversion](#L
 
         // local departure time in phoenix is 11 pm on March 30 2005 
         // (ny changes to dst on apr 3 at 2 am)
-        auto phx_departure = day_point(2005_y/mar/30) + 23h + 0min;
+        auto phx_departure = sys_days(2005_y/mar/30) + 23h + 0min;
         auto utc_departure = phx_tz->to_sys(phx_departure);
 
         auto flight_length = 4h + 30min;
@@ -557,9 +557,9 @@ an example using the IANA timezone database see the [Local to UTC Conversion](#L
         using namespace date;
 
         auto nyc_tz = locate_zone("America/New_York");
-        auto nyc_time = day_point(2004_y/oct/4) + 12h + 14min + 32s;
+        auto nyc_time = sys_days(2004_y/oct/4) + 12h + 14min + 32s;
         std::cout << nyc_time << '\n';
-        auto time_t_epoch = day_point(1970_y/1/1);
+        auto time_t_epoch = sys_days(1970_y/1/1);
         std::cout << time_t_epoch << '\n';
 
         // first convert nyc_time to utc via the utc_time()