Remove explicit default destructors (#157)

From CppCoreGuidelines:

Rule of Zero: C.20: If you can avoid defining default operations, do.
C.52: Use inheriting constructors to import constructors into a derived class that does not need further explicit initialization.
DRY forward and using declarations.
Miscellaneous:

Fix format.sh to output examples with normalised paths in sorted order.

Co-authored-by: ArthurSonzogni <sonzogniarthur@gmail.com>

src/ftxui/dom/hbox.cpp

@@ -13,7 +13,6 @@ namespace ftxui {
 class HBox : public Node {
  public:
   HBox(Elements children) : Node(std::move(children)) {}
-  ~HBox() {}
 
   void ComputeRequirement() override {
     requirement_.min_x = 0;