How unit and race creation works in Globulation 2
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(c) 2001 Luc-Olivier de Charriere and Stephane Magnenat

Properties
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Each Unit in the game has a type, this type specify its characteristics. Each team has differents types because the race (the ensemble of types) can be customized.
So we have the following types :

- EntityType : Generic class for loading constant from a text file.
- UnitType : A type for units for a team (ex: the explorer of Luc, the warrior of Stephane)
- Race : the collection of all unittypes for a team (here 3 unittypes : explorer, worker & warrior)


How they act
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If a unit is behond a critical ceiling :
	- eating
	- healing
If a unit is free :
	- harvesting food
	- upgrade itself
	- harvesting for construction
	- upgrading buildings
	- meeting (flag)
