Calculation of a node's length; auxiliary functions; tests
Minor changes; length to width
Main function can print leaves correctly

* fn to calculate the height of a tree.
* fns to make empty nodes to have a tree whose leaves are
at the same level.
* Using fake nodes, it is easier to print the leaves at
their right place.
Printing root better, we can see the tree

* It is necessary to print the path between roots
and branches.