Use automated exercise/testing

@NelleV pointed out that it's very useful for students to get automated feedback on their exercises — we should find a way (probably pre-existing e.g. nbgrader) to make exercise solutions testable automatically.

The issue names no files or tests; start by reviewing the exercise materials and evaluating the suggested nbgrader approach. Done means selecting and documenting an automated feedback and testing path that can run against exercise solutions.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.