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>

include/ftxui/dom/node.hpp

@@ -14,7 +14,7 @@ class Node;
 class Screen;
 
 using Element = std::shared_ptr<Node>;
-using Elements = std::vector<std::shared_ptr<Node>>;
+using Elements = std::vector<Element>;
 
 class Node {
  public: