Simplifications and commenting of alien exercise for CodeClub.
More tweaks.
Moving some stuff into a separate file.
More tweaks.
Renames.
Clearer variable names.
Another tweak. Localising image loading. Needed some file rearrangement.
Removing redundant lines.
Hiding some complexity in data loader.
More locality of reference in sprite classes.
More comments.
Updated Word doc.
More Word doc updates.