message: Update: update C++ API's readme and modify datasets' filepath
diff: @@ -390,7 +390,12 @@ The HTTP API of gStore is placed in api/http directory in the root directory of
  - client.h
  - - example.cpp (small example program to show the basic idea of using the C++ API)
  + - example/ (small example program to show the basic idea of using the C++ API)
  + - example.cpp
  +
  + - Benchmark.cpp
  +
  + - Makefile
  - Makefile (compile and build lib)
  @@ -413,19 +418,19 @@ CHttpClient hc;
  string res;
  int ret;
  // build a new database by a RDF file.
  -ret = hc.Get("127.0.0.1:9000/build/lumb/data/LUBM_10.n3", res);
  +ret = hc.Get("http://127.0.0.1:9000/?operation=build&db_name=lubm&ds_path=data/lubm/lubm.nt", res);
  cout&lt;&lt;res&lt;&lt;endl;
  // load databse
  -ret = hc.Get("127.0.0.1:9000/load/lumb", res);
  +ret = hc.Get("http://127.0.0.1:9000/?operation=load&db_name=lumb", res);
  cout&lt;&lt;res&lt;&lt;endl;
  // then you can execute SPARQL query on this database.
  -ret = hc.Get("127.0.0.1:9000/query/data/ex0.sql", res);
  +ret = hc.Get("http://127.0.0.1:9000/?operation=query&format=json&sparql=data/lubm/lubm_q0.sql", res);
  cout&lt;&lt;res&lt;&lt;endl;
  // output information of current database
  -ret = hc.Get("127.0.0.1:9000/monitor", res);
  +ret = hc.Get("http://127.0.0.1:9000/?operation=monitor", res);
  cout&lt;&lt;res&lt;&lt;endl;
  // unload this databse
  -ret = hc.Get("127.0.0.1:9000/unload", res);
  +ret = hc.Get("http://127.0.0.1:9000/?operation=unload&db_name=lubm", res);
  cout&lt;&lt;res&lt;&lt;endl;
  ```
  