April 10: Added feature to set the maximum number of enemies, bug fixes.

[Content Additions / Specification Changes]

1. Added a feature to set the maximum number of enemy spawns via the options menu. If the number of enemies exceeds this maximum, the other enemies will be made stronger.

[Bug Fixes]

1. Fixed an issue where soldiers would become invisible if the destroyed building was dismantled while they were still inside.
2. Fixed a bug where allied units would get stuck in MOD buildings. This was caused by a feature that altered movement speed on buildings to implement "Abatis", which inadvertently set movement speed to zero on MOD buildings.
3. Fixed an issue where the selected Skybox option in the settings dropdown would always display "Japanese-style room" when reopening the settings menu, regardless of the actual saved setting.