Feature/date time mstimer clock (#861)

* Added daylight savings time calculation module with unit testing.

* Added datetime daylight savings time and clock API

* Added basic datetime_local() clock using mstimer as basis and time-sync option.  Integrated clock with ports/stm32f4xx example.

src/bacnet/basic/sys/dst.h

@@ -0,0 +1,58 @@
+/**
+ * @file
+ * @brief This file contains the function prototypes for for the module.
+ * @author Steve Karg <skarg@users.sourceforge.net>
+ * @date 1997
+ * @note Public domain algorithms from ACM
+ * @copyright SPDX-License-Identifier: CC-PDDC
+ */
+#ifndef BACNET_BASIC_SYS_DST_H
+#define BACNET_BASIC_SYS_DST_H
+#include <stdint.h>
+#include <stdbool.h>
+/* BACnet Stack defines - first */
+#include "bacnet/bacdef.h"
+
+struct daylight_savings_data {
+    bool Ordinal : 1;
+    uint8_t Begin_Month;
+    uint8_t Begin_Day;
+    uint8_t Begin_Week;
+    uint8_t End_Month;
+    uint8_t End_Day;
+    uint8_t End_Week;
+    uint16_t Epoch_Year;
+    uint8_t Epoch_Day;
+};
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+bool dst_active(
+    struct daylight_savings_data *dst,
+    uint16_t year,
+    uint8_t month,
+    uint8_t day,
+    uint8_t hour,
+    uint8_t minute,
+    uint8_t second);
+void dst_init(
+    struct daylight_savings_data *data,
+    bool automatic,
+    uint8_t begin_month,
+    uint8_t begin_day,
+    uint8_t begin_which_day,
+    uint8_t end_month,
+    uint8_t end_day,
+    uint8_t end_which_day,
+    uint8_t epoch_day,
+    uint16_t epoch_year);
+/* initialization */
+void dst_init_defaults(struct daylight_savings_data *data);
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif