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"),