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.
|hbox| and |vbox| are similar. They are just the same component, but
drawing in a different direction.
This patchs factorize the layout logic. Goal is to reduce code size and
reuse it for the |gridbox| dom element.
Bug: https://github.com/ArthurSonzogni/FTXUI/issues/114