Added test case for sequence diagram with multiple translation units

tests/t20014/t20014.cc

@@ -0,0 +1,23 @@
+#include "include/t20014.h"
+#include "include/t20014_b.h"
+#include "include/t20014_c.h"
+
+namespace clanguml {
+namespace t20014 {
+
+void log(const char *msg) { }
+
+int tmain()
+{
+    B b;
+    C<B, int> c;
+
+    b.b1(0, 1);
+    b.b2(1, 2);
+
+    c.c1(2, 3);
+
+    return 0;
+}
+}
+}