message: Added default move constructor and assignment operator for tstring.
  Also, minor cleanup of methods.
diff: @@ -49,9 +49,9 @@ class tstring {
  std::string str_;
  public:
  - tstring() : str_() {}
  + tstring() = default;
  - tstring(const tstring& str) = default;
  + tstring(const tstring&) = default;
  tstring(const std::string& str) : str_(str) {}
  @@ -63,7 +63,9 @@ class tstring {
  std::is_same<T, absl::string_view>::value, T>>
  explicit tstring(const T& str) : str_(str.data(), str.size()) {}
  - ~tstring() {}
  + tstring(tstring&&) noexcept = default;
  +
  + ~tstring() = default;
  tstring& operator=(const tstring& str) = default;
  @@ -87,6 +89,8 @@ class tstring {
  return *this;
  }
  + tstring& operator=(tstring&&) noexcept = default;
  +
  bool operator<(const tstring& o) const { return str_ < o.str_; }
  bool operator>(const tstring& o) const { return str_ > o.str_; }
  