Add `all-your-base`

[BNAndras]

Problem specification: https://github.com/exercism/problem-specifications/tree/main/exercises/all-your-base

TODO:

• Generate the exercise files with ./bin/fetch-configlet && ./bin/configlet create --practice-exercise all-your-base.
• Add your GitHub username as a string to the "authors" array in ./exercises/practice/all-your-base/.meta/config.json.
• Add ./exercises/practice/all-your-base/src/all-your-base.app.src. Check other exercises for examples.
• Copy rebar.config, rebar.lock, and Makefile from another exercise folder into ./exercises/practice/all-your-base/.
• Populate ./exercises/practice/all-your-base/test/all-your-base-tests.lfe with the tests from the problem specification.
• Solve the exercise using ./exercises/practice/all-your-base/src/all-your-base.lfe.
• When tests pass for your solution, copy your solution into ./exercises/practice/all-your-base/.meta/example.lfe. Replace the contents of ./exercises/practice/all-your-base/src/all-your-base.lfe with a stub implementation. Check other exercises for an example.
• Update the auto-populated exercise difficulty in ./config.json for this exercise.