add morphism for unix-timestamp to iso8601

morphisms/timepoint.morphism-base

@@ -0,0 +1,15 @@
+```
+#include <time.h>
+```
+
+morph_unixtime_to_iso ()
+      TimePoint ~ <TimeSince UnixEpoch> ~ Duration ~ Seconds ~ ℝ ~ <QuantizedLinear 0 1 1> ~ ℕ ~ x86.UInt64
+-->   TimePoint ~ ISO8601 ~ <Seq~<ValueTerminated 0> Char~Ascii~x86.UInt8>
+```
+    time_t rawtime = (time_t)(*src);
+    struct tm *timeinfo = gmtime(&rawtime);
+    if (!timeinfo) return -1;
+
+    strftime((char*)dst, 20, "%Y-%m-%dT%H:%M:%SZ", timeinfo);
+    return 0;
+```