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'

example/cat/main.zig

@@ -41,7 +41,7 @@ fn usage(exe: []const u8) !void {
     return error.Invalid;
 }
 
-fn cat_file(stdout: &os.File, file: &os.File) !void {
+fn cat_file(stdout: *os.File, file: *os.File) !void {
     var buf: [1024 * 4]u8 = undefined;
 
     while (true) {