Implement opt Q for fixed-point precision, and q literals (e.g. 12.34q8) (#958)

Fixes #957

Co-authored-by: ISSOtm <eldredhabert0@gmail.com>

test/asm/opt-Q.asm

@@ -0,0 +1,18 @@
+MACRO test
+	PUSHO
+	OPT Q\1
+	print STRFMT("Q%4s", "\1")
+	def n = 1.14159
+	println STRFMT(" -> %032b", n)
+	POPO
+ENDM
+
+	for x, 1, 32
+		if x < 16
+			test .{d:x}
+		else
+			test {d:x}
+		endc
+	endr
+	test .0 ; error
+	test 32 ; error