Switch from parentheses to angle brackets

`\(` is more likely to be a valid escape sequence in the
future (as is `\[`) and `\{` is already taken.

test/asm/bracketed-macro-args.asm

@@ -0,0 +1,19 @@
+MACRO printargs
+	PRINTLN "first = \<1>"
+	FOR I, 2, _NARG
+		PRINTLN "next = \<{d:I}>"
+	ENDR
+	PRINTLN "last = \<{d:_NARG}>"
+ENDM
+
+	printargs A, B, C, D
+
+MACRO mac
+	println \<2__> + \<1_2> + \<\1>
+x = 2
+	println \<{d:x}> + \<1_{d:x}> + \<\<\<13>>>
+y equs "NARG"
+	println \<x> + \<1_{d:x}_> + \<\<\<_{y}>>>
+ENDM
+
+	mac 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 1