Replace `alias` with `alias_method`

Done with `rubocop --auto-correct --only Alias`
Standardise indentation of access modifiers

Done with `rubocop --auto-correct --only AccessModifierIndentation`
Replace "and" & "or" with preferred versions

Done with `rubocop --auto-correct --only AndOr`
Replace attr with attr_reader

Done with `rubocop --auto-correct --only Attr`
Fix a number of do/end/{/} block style issues

Done with `rubocop --auto-correct --only Blocks`

A large number remain unfixed
Standardise on collection methods

Done with `rubocop --auto-correct --only CollectionMethods`