* speed up vector assignment, test=develop

* update op_desc with c-string, test=develop

* update compatible_pb.cc, test=develop

* using unique_ptr in fbs::desc, test=develop

* add fbs to compatible_pb, test=develop

* update model_parser functions, test=develop

* fix bugs, test=develop

* add view suffix to read-only classes for flatbuffers, test=develop

* add some write-apis for flatbuffers, test=develop

* update desc interfaces, test=develop

* update desc interfaces, test=develop

* update compatible_pb.cc, test=develop

* fix build errors, test=develop

* remove the fstream to shrink the size of library, test=develop

* add flatbuffers, test=develop

* fix cmake codes, test=develop