Saving progress for review of draft chapter still needs helper functions

[Tristan-Raz]

Draft chapter for the recursion portion of the Java code to fix issue #29. This helps explain some example recursion in both languages with some active code. It is still missing a helper function, but it will be added in the next push. It also shows the difference in error messages and handling.

Pair programmed with @coco3427

[pearcej]

I really appreciate this work!

Please update this branch before working on it any more.

I made some minor changes because I think it is critically important to make everything as parallel as possible to make learning easier.

Please try to use line-by-line conversions as much as possible.

I am likely to add a class-based Python implementation before the Java one since that is also possible.

In the current section 2, there is a misunderstanding about what helper methods are. For better understanding, see https://stackoverflow.com/questions/75690272/why-do-binary-tree-traversals-need-a-helper-function and https://www.geeksforgeeks.org/java/recursion-in-java/, but do not copy or use the examples from these sources. @coco3427 should be able to help with ideas for a REAL helper method.