Update World#attack tests.
Merge branch 'bug/battle'
Prune countries which are too large/small.
Add core.clamp function.
Tweak map generation.
Add Country#size.
Prune the neighbouring countries that have been culled.
Find the largest island.
Refactor world builder.
Extract voronoi module.
Move traverse function into core module.
Tweak minimum country size.
Cleanups.
Update AI to always choose the target country with the least armies.
Merge branch 'feature/prune-countries'
Only reinforce a player with the number of armies in the largest player island.
Extract island module.
Extract graph module.
Cleanups.
Update fkit dependency.