parser,fmt: implement [manualfree] module abc for opting out *all* fns in a given .v from autofree

vlib/v/fmt/tests/manualfree_keep.v

@@ -0,0 +1,18 @@
+[manualfree]
+module main
+
+fn abc() {
+	x := 'abc should be autofreed'
+	println(x)
+}
+
+[manualfree]
+fn xyz() {
+	x := 'xyz should do its own memory management'
+	println(x)
+}
+
+fn main() {
+	abc()
+	xyz()
+}