* bencode: add type comment;
* object: delete obj_unset api function;
* object: move object struct to header file;
* bencode: remove using memcpy;
* bencode: remove string.h and stdio.h;
* bencode: change return type bc_read_string api function to size_t;
* bencode: change return type bc_read_int api function to size_t;
* bencode: change type len string to size_t in bc_read_string;