use * for pointer type instead of &

See #770

To help automatically translate code, see the
zig-fmt-pointer-reform-2 branch.

This will convert all & into *. Due to the syntax
ambiguity (which is why we are making this change),
even address-of & will turn into *, so you'll have
to manually fix thes instances. You will be guaranteed
to get compile errors for them - expected 'type', found 'foo'

test/cases/struct_contains_null_ptr_itself.zig

@@ -2,13 +2,13 @@ const std = @import("std");
 const assert = std.debug.assert;
 
 test "struct contains null pointer which contains original struct" {
-    var x: ?&NodeLineComment = null;
+    var x: ?*NodeLineComment = null;
     assert(x == null);
 }
 
 pub const Node = struct {
     id: Id,
-    comment: ?&NodeLineComment,
+    comment: ?*NodeLineComment,
 
     pub const Id = enum {
         Root,