Check user's version of Odin executables

[gvrooyen]

Since Odin has monthly and nightly builds, it might be worthwhile to have a script that checks if you have Odin installed and whether it's outdated. If so, it can download the correct version from GitHub. (@BNAndras)

The test.yml GitHub Action is configured to test the solution against a very specific Odin version (down to the commit hash), and this will also be the version against which Exercism users' solutions will be tested. Possible ways in which we can help contributors to test against the same version are:

1. Add a fetch-odin script that can fetch, build, and install the reference version of the compiler.
2. Let the fetch-odin --check-version / fetch-odin -c script compare the installed version with the reference version, and indicate whether an update is needed.
3. Let run-tests.sh give an INFO message if the currently installed Odin version is newer than the reference, and a WARNING if it is older.