Add a free four-byte slot to the entity structure

Whoa. You can do some pretty cool stuff with this:

<b>Engine structure format</b>

0 - generic*
	0 - target*
	1 - targetname$
	2 - triggermode%
	3 - targetdelay%
1 - physics*
	0 - velocityx#
	1 - velocityy#
	2 - velocityz#
	3 - mass#
	4 - friction#
	5 - flags%
2 - behavior*
	0 - class

	This structure varies depending on entity class.

	<b>Classes</b>
	
	Flare
	0 - range#
	1 - color%

	Player
	0 - name$
	1 - health%

GetEntityTarget()
GetEntityTargetname$()
GetFlareRange#()

etc...