[v0.2.3] Rewrote `engine/core.rb`
[v0.2.3] Rewrote `engine/core.rb`

Fixed bug with `core.rb` retrieving modules

[Bug] To solve possible duplicate `ClassNo` but different `LessonType` or other variables

Signed-off-by: Kenneth Ham <69c8000bdf31eeda65453a41b789fbb847fb180d@comp.nus.edu.sg>

nusmodifications/nusbot