This implement the flexbox elements, following the HTML one.
Built from them, there is also the following elements:
- `paragraph`
- `paragraphAlignLeft`
- `paragraphAlignRight`
- `paragraphAlignCenter`
- `paragraphAlignJustify`
This is a breaking change.
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>
