message: Add char * overload for FlatBufferBuilder::CreateString()
  Without this change, the compiler tries to select the following overload
  when CreateString is passed a `char *`:
  template<typename T>
  Offset<String> CreateString(const T &str) {
  return CreateString(str.c_str(), str.length());
  }
  which is not valid since char pointers don't have methods.
  (Fixes
diff: @@ -1001,6 +1001,13 @@ class FlatBufferBuilder {
  return CreateString(str, strlen(str));
  }
  + /// @brief Store a string in the buffer, which is null-terminated.
  + /// @param[in] str A char pointer to a C-string to add to the buffer.
  + /// @return Returns the offset in the buffer where the string starts.
  + Offset<String> CreateString(char *str) {
  + return CreateString(str, strlen(str));
  + }
  +
  /// @brief Store a string in the buffer, which can contain any binary data.
  /// @param[in] str A const reference to a std::string to store in the buffer.
  /// @return Returns the offset in the buffer where the string starts.
  