Added String examples.

src/Examples/StringExampleGetAllocatedSize.cpp

+#include <iostream>
+
+using namespace TNL
+       
+int main()
+{
+    String str("my world")
+    int alloc_size = str.getAllocatedSize();
+    cout << "alloc_size:" << alloc_size << endl;
+}
\ No newline at end of file

src/Examples/StringExampleGetSize.cpp

+#include <iostream>
+
+using namespace TNL
+       
+int main()
+{
+    String str("my world")
+    int size = str.getSize();
+    cout << "size of string:" << size << "bytes" << endl;
+}
+

src/Examples/StringExampleSetSize.cpp

+#include <iostream>
+
+using namespace TNL
+       
+int main()
+{
+    int memory 
+    memory.setSize( 256 );
+    cout << "memory:" << memory << endl;
+}