Added a solution for laying out binary trees

Also added the tree used in the examples
Removed unneeded alias, renamed parameter
Improve the presentation of "Layout a binary tree" (99 problems)
Add a solution to "Layout a binary tree" (99 problems)
Update index.md

fix: typo
Update index.fr.md
Merge remote-tracking branch 'upstream/master' into graph_algorithms
reposition narrative before the code block