Added test case for sequence diagram with multiple translation units

tests/t20014/include/t20014_c.h

@@ -0,0 +1,19 @@
+#pragma once
+
+namespace clanguml {
+namespace t20014 {
+
+template <typename T, typename F> struct C {
+    F c1(F i, F j) {
+        return c_.b1(i, j);
+    }
+
+    F c2(F i, F j){
+        return c_.b2(i, j);
+    }
+
+    T c_;
+};
+
+}
+}