Problem: Expected text for interactive marks is in a separate json file
from the tutor file. When the tutor file is updated, line numbers
(potentially many) have to be updated in the json file. This is a
burden for maintenance and automatic testing.
Solution: Put the expected text inline in the tutor file, marked
with `[[]]`. Parse and remove the comments before opening the tutor
file so extmarks can be applied.
1. Every hyperlink-like element was replaced by `"$1"` (where $1 is the original string showed in the hyperlink);
2. Arrows `--->` were used in lines containing practice examples when no editing text is involved;
3. Context on interactivity was minimally adapted when strictly needed, not to disrupt the original tutor's intent;
4. Tests regarding the tutor file refactored to ensure the new syntax is not flagged as an error.
