Document and label some duel functions

Author: ElectroDeoxys

src/constants/duel_constants.asm

@@ -161,8 +161,8 @@ DEF SUBSTATUS2_UNABLE_RETREAT EQU $09
 DEF SUBSTATUS2_BONE_ATTACK    EQU $0b
 DEF SUBSTATUS2_GROWL          EQU $12
 
-DEF SUBSTATUS3_THIS_TURN_DOUBLE_DAMAGE EQU 0
-DEF SUBSTATUS3_HEADACHE                EQU 1
+DEF SUBSTATUS3_THIS_TURN_DOUBLE_DAMAGE_F EQU 0
+DEF SUBSTATUS3_HEADACHE_F                EQU 1
 
 ; DUELVARS_ARENA_CARD_FLAGS constants
 DEF USED_PKMN_POWER_THIS_TURN_F EQU 5
@@ -236,6 +236,7 @@ DEF NO_DAMAGE_OR_EFFECT_NSHIELD      EQU $05
 	const OPPACTION_USE_METRONOME_ATTACK      ; $14
 	const OPPACTION_6B15                      ; $15
 	const OPPACTION_DUEL_MAIN_SCENE           ; $16
+DEF NUM_OPP_ACTIONS EQU const_value
 
 ; constants for PracticeDuelActionTable entries
 	const_def 1