Addendum to Rusty Roguelike Bevy

Points to be explained:

• Skipped and Merged steps
• Difference in querying entities having components between Legion and Bevy (e.g. let base_damage)

Linguistic improvements:

• PointC destructuring
• State machine via const generics
• .find_map(|blah| (blah == 1).then(|| item_entity))
• Create Hashset from iterable: HashSet::from(["Einar", "Olaf", "Harald"])
• Add entires to an array via: available_entities.extend(vec![t; t.frequency as usize]);