Add timespec -- add tests for it too.

include/timespec.h

@@ -0,0 +1,46 @@
+#pragma once
+#include "mgos.h"
+
+/* A simple time specifier for windows of time throughout a 24 hour day.
+ *
+ * Callers construct a struct mgos_timespec and then add time range
+ * specifications to the object. Ranges consist of ':', '-' and [0-9]
+ * characters and describe a [start-stop> time range where 'start' is
+ * included but 'stop' is not. Start and stop can have hours, minutes
+ * and seconds separated by ':'. Example specs:
+ *    "8:00-10:00"   (from 8am to 10am -- 7200 seconds)
+ *    "23-01"        (from 11pm to 1am -- 7200 seconds)
+ *    "01:02:03-02"  (from 01:02:03 to 2am -- 3477 seconds)
+ *
+ * Example to demonstrate the usage:
+ *
+ * struct tm target;
+ * struct mgos_timespec *ts = timespec_create();
+ * timespec_add_spec(ts, "8:00-10:00");       // 7200 seconds, [08:00:00 - 10:00:00>
+ * timespec_add_spec(ts, "23-01");             // 7200 seconds, [23:00:00 - 01:00:00>
+ * timespec_add_spec(ts, "01:02:03-02:03:04"); // 3661 seconds, [01:02:03 - 02:03:04>
+ *
+ * target.tm_hour=8; target.tm_min=0; target.tm_sec=0;  // 08:00:00
+ * timespec_match(ts, &target); // TRUE; start of first spec
+ *
+ * target.tm_hour=10; target.tm_min=0; target.tm_sec=0; // 10:00:00
+ * timespec_match(ts, &target); // FALSE; end of first spec; end times are excluded!
+ *
+ * target.tm_hour=0; target.tm_min=0; target.tm_sec=0; // 00:00:00
+ * timespec_match(ts, &target); // TRUE; in the middle of the second spec
+ *
+ * target.tm_hour=1; target.tm_min=2; target.tm_sec=3; // 01:02:03
+ * timespec_match(ts, &target); // TRUE; the first second of the third spec
+ *
+ * target.tm_hour=2; target.tm_min=3; target.tm_sec=3; // 02:03:03
+ * timespec_match(ts, &target); // TRUE; the last second of the third spec
+ *
+ * timespec_destroy(&ts);
+ */
+
+struct mgos_timespec;
+
+struct mgos_timespec *timespec_create();
+bool timespec_destroy(struct mgos_timespec **ts);
+bool timespec_add_spec(struct mgos_timespec *ts, const char *spec);
+bool timespec_match(const struct mgos_timespec *ts, const struct tm *tm);