chore: add tests and CI

.gitignore

.gitlab-ci.yml

Dockerfile

Makefile

export-apkgs-test-runner/Dockerfile

test/fixtures/anki/.apkg-spec.yaml

test/fixtures/anki/Test.apkg

test/fixtures/csv/.apkg-spec.yaml

test/fixtures/csv/content.csv

test/fixtures/csv_updated_content/.apkg-spec.yaml

test/fixtures/csv_updated_content/content.csv

test/fixtures/templates/q_a/.template-spec.yaml

test/fixtures/templates/q_a/q_a/back.html

test/fixtures/templates/q_a/q_a/front.html

test/fixtures/templates_updated/q_a/.template-spec.yaml

test/fixtures/templates_updated/q_a/q_a/back.html

test/fixtures/templates_updated/q_a/q_a/front.html

test/test_export_apkgs.py