Implement hexagram_anim_duration()

src/anim.c

@@ -87,3 +87,14 @@ int hexagram_anim_step(hexagram_anim *anim, hexagram_anim_progress_fn *fn) {
 
     return 1;
 }
+
+double hexagram_anim_duration(hexagram_anim *anim) {
+    double ret = 0.0;
+    size_t i;
+
+    for (i=0; i<anim->count; i++) {
+        ret += anim->stops[i].duration;
+    }
+
+    return ret;
+}