[bat] change comment token to @rem

[septsea]

I often edit batch files using VS Code. However, there is something that I think that can be optimized.

When I press Ctrl+/ to comment one line, I expect it to prepend @REM instead of REM to the line.

REM remark prints itself, while @REM remark does not.

I know that using @echo off is a workaround; I could replace all REM s by @REM s as well.

However, either needs extra work, which is somewhat inconvenient.