RGBDS syntax updates (#905)

New MACRO and DEF syntax

engine/events/field_moves.asm

@@ -1,6 +1,6 @@
-FIELDMOVE_GRASS EQU $80
-FIELDMOVE_TREE EQU $84
-FIELDMOVE_FLY EQU $84
+DEF FIELDMOVE_GRASS EQU $80
+DEF FIELDMOVE_TREE  EQU $84
+DEF FIELDMOVE_FLY   EQU $84
 
 PlayWhirlpoolSound:
 	call WaitSFX