Tooling and CI set up + 1st four exercises (#25)

[gvrooyen]

• hello-word, leap, configuration updates

Completed the hello-world and leap exercises.
Updated configuration.

• Add workflow in test.yml

• Modified CI workflow to build Odin from source

• Completed difference-of-squares, added format-all

Completed the difference-of-squares practice exercise, and added the bin/format-all.sh script that recursively searches for .odin files and runs odinfmt on them.

• Formatted source, added formatting to webhook

All source files have been reformatted with the odinfmt.json spec. bin/format-all.sh is now run automatically on commit.

• Added step to push autoformatting changes

The test.yml GitHub workflow now pushes any changes that it makes, so that they persist in the repo.

• Modified test.yml to not fail on no formatting

test.yml now only attempts a commit and push if the automated formatting actually changed any files.

• Added missing dashes in argument

• Fixed bin/verify-exercises

The verify-exercises script now runs the individual test for both concept and practice exercises, and is the default in the GitHub workflow.

• Added the "grains" exercise

Tests were lifted from the Gleam track.

• Updated README; fixed test verification

• The README now contains more thorough instructions on how to add a new exercise.
• Fixed a variable name in the test runner that caused the "test all solutions" loop to run multiple times when verifying solutions.

• Formatted config files with configlet

• Fixed testing bug that clobbered stub solutions

• Fixed bin/run-test.sh so that it doesn't delete the stub solution when a test fails.
• Restored exercises, and added a NotImplemented error condition for the stubs.

• Small code fixes. Updated README.

• Ran the code formatter on source files.
• Rehaul of the README to follow Python's example.

• Added resistor-color exercise. Updated README.

• Fixed and tested the test.yml action

The workflow now uses a fixed commit hash to pull a specific release of Odin. We now use Ubuntu 22.04 which has the libffi8 dependency, and add clang as the only other dependency.

• Implemented the resistor-color exercise

• Removed configlet dependency in test.yml

• Moved the exercise checklist to a linked GH issue

• Test runner now checks that stub solution fails

Added a check to bin/run-test.sh so that verifies that the stub solution does not pass any tests. Fixed hello-world.odin to actually be a stub.

• Fixed incorrect stubs, added panics for stub procs

• Improved bin/run-test.sh to add more visible color coding to the output.
• Replaced NotImplemented error codes with a compile-time panic for procedures that have not yet been implemented.
• Fixed stubs that were actually complete examples.

• Removed fancy terminal color commands

• Added support for skipping and unskipping tests

• Exercises' unit tests were modified so that only a minimal subset of tests are initially enabled; the rest are skipped.
• The test runner was modified to automatically unskip all test cases before running the tests.

• Removed mention of NotImplemented in the README