Fix Markdown

index.md must be html, not md in html <div> clause

Add definition of hardcoding #143

Can edit pages from MkDocs rendered site, thanks @bclaremar

Reflect

Update Optimization lesson

Merge 'struct design' back into 'data structures'

Fix links

Give feedback t students, ignore spelling due to GH SHA values, progr…

…ess #10

Merge branch 'main' of https://github.com/UPPMAX/programming_formalisms