ACO Refactoring/Cleanup

[Quincunx271]

From #153 , some PR review ideas were suggested to be brought up in the future. Some of these are more broad than just ACO:

• Move #define to constexpr: Aco paper branch apr2021 #153 (comment)
• Convert iteration to use the external STL-style iterators: Aco paper branch apr2021 #153 (comment)
• Use override on overridden functions: Aco paper branch apr2021 #153 (comment)