Change reverse method signature to follow test requirements

Update CONTRIBUTING.md

Add details of README.md to description of submodule.

Add details of how to generate README.md to section on
how to implement new exercise.

markdown: add to track

Nix public access

Ignore build.gradle when CI runs tests against changeset

* make classes and methods package private #1052

* method accessor changes

This reverts commit 58ed692a57b235d3ab3f8bb68e9375287eff8e47.

This reverts commit b14f3aef3d60abc5964b0224b3ddbd006e66d95d.

removing public access modifier from IsogramChecker class and methods

Fixes #1055 

* make classes and methods package private #1055

* changed nested class to public

* made Element<T> private and its constructor package-private

grade-school: make classes and methods package private in reference solution

trying something else

* Temporary commit to test journey test fix

* Fix journey test

Make sure run-journey-test-from-ci doesn't try to run settings.gradle as
an exercise.

* Revert "Temporary commit to test journey test fix"

This reverts commit eb0d5dd091d8f3c633fcda7742312a2c261bff8b.

maintainers.json: add @sjwarner-bp

etl: remove public access modifier from etl

clock: make classes and methods package private in reference solution

accumulate: make classes and methods package private in reference solution

binary: make classes and methods package private in reference solution

reverse-string: change unlocked_by exercise to two-fer

fix broken links in maintaining.md

reverse-string: add to track