Docs: add `maxdepth=100` arg to print_tree

[IanButterworth]

Without this it's common to get truncation because the default is 5.

And discoverability isn't great because AbstractTrees.print_tree isn't documented https://juliacollections.github.io/AbstractTrees.jl/stable/search/?q=print_tree but has a docstring that shows this arg https://github.com/JuliaCollections/AbstractTrees.jl/blob/af3fabd36631efe361bc8e1ba45f9b84e898b459/src/printing.jl#L17

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 82.84%. Comparing base (622b233) to head (89ae8b8). Report is 17 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #394 +/- ## ========================================== + Coverage 78.96% 82.84% +3.87% ========================================== Files 17 12 -5 Lines 2054 1784 -270 ========================================== - Hits 1622 1478 -144 + Misses 432 306 -126 ```

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[timholy]

Thanks!