Parentheses in macro args prevent commas from starting new arguments

This is similar to C's behavior, and convenient for passing
function calls as single values, like `MUL(3.0, 4.0)` or
`STRSUB("str", 2, 1)`.

Fixes #704

test/asm/macro-arg-parentheses.asm

@@ -0,0 +1,19 @@
+MACRO printargs
+	REPT _NARG
+		PRINTLN \1
+		SHIFT
+	ENDR
+ENDM
+
+	printargs mul(3.0, 4.0)
+
+MACRO printlit
+	REPT _NARG
+		PRINTLN "\1"
+		SHIFT
+	ENDR
+ENDM
+
+	printlit a(b,c\,d), ((e,f),g), ))h, i\,j,
+	printlit \(k, l), (m:\)n,o(p)q), (r,s)t
+	printlit "))u,v(", ("w,x","y,z"),

test/asm/macro-arg-parentheses.out

@@ -0,0 +1,11 @@
+$C0000
+a(b,c,d)
+((e,f),g)
+))h
+i,j
+(k
+l)
+(m:)n,o(p)q)
+(r,s)t
+"))u,v("
+("w,x","y,z")

test/asm/raw-macro-args.asm

@@ -22,7 +22,7 @@ STR EQUS "str\"ing"
 	printargs "literal \"\\\"", \ ; comment 2
 """multi-"line"
   ""string"" arg"""
-	printargs MUL(2.0\, 3.0)
+	printargs MUL(2.0, 3.0)
 	printargs "unclosed
 
 	printlit NUM
@@ -32,7 +32,7 @@ STR EQUS "str\"ing"
 	printlit "literal \"\\\"", \ ; comment 4
 """multi-"line"
   ""string"" arg"""
-	printlit MUL(2.0\, 3.0)
+	printlit MUL(2.0, 3.0)
 	printlit this\n is\, \{not\} a\\n syntax\" error
 	printlit "unclosed
 	printlit """EOF