Spring RTS Engine

Proposed: Two tags that change the experience a unit needs to level up and the experience a unit gives to others when hit. ExpValue would be used instead of cost for figuring out how much experience to give an attacker for hitting this unit while ExpNeed would be used instead of cost for figuring out what veterancy that experience equals.

This would allow finer adjustment of the experience system to suit a mod's purpose.

Optimally the gains for experience could be controlled by the mod as well instead of the hardcoded accuracy, HP and whatnot gains.