message: replaced custom mesage for standardised message
diff: namespace NovelRT::Exceptions {
  class CharacterNotFoundException final : public std::runtime_error {
  public:
  - CharacterNotFoundException(const std::string &message, const char c) :
  - std::runtime_error(message +" character: " + c)
  + CharacterNotFoundException(const char c) :
  + std::runtime_error(std::string("Unable to return specified character: ") + c)
  {}
  };
  }
  