- extended the grammar so that the DECORATE function declaration list can almost be used as-is, with the sole exception of requiring any action function to declare a return type, even if it is void.

This adds:
 * builtin types color, state and sound.
 * ending a parameter list with an ellipsis to declare a varargs list. (A_Jump uses this.)
 * allowing to declare optional arguments by giving them a default value.
 * adding an 'action' qualifier for function declarations.

src/zscript/zcc_parser.h

@@ -119,6 +119,11 @@ enum EZCCBuiltinType
 	ZCC_Vector3,
 	ZCC_Vector4,
 	ZCC_Name,
+
+	ZCC_Color,		// special types for ZDoom.
+	ZCC_State,
+	ZCC_Sound,
+
 	ZCC_UserType,
 
 	ZCC_NUM_BUILT_IN_TYPES
@@ -437,6 +442,7 @@ struct ZCC_LocalVarStmt : ZCC_Statement
 struct ZCC_FuncParamDecl : ZCC_TreeNode
 {
 	ZCC_Type *Type;
+	ZCC_Expression *Default;
 	ENamedName Name;
 	int Flags;
 };