Allow 'alf' as query language.
Rename solutions -> answers student-side.
Let Submission be a class, not a module.
Rename fixtures/validator -> fixtures/submissions.
Reorganize XML support for submissions
Add data extractor from XML submissions.
Database infrastructure + initial schema + seeds.
Add import command.
Add .gitignore.
Allow empty expressions in XML files, but ignore answer.
Recognize Path instances in xmldoc_for.
Add a check helper command.