MiSTer top cover with Fan guard

I added a fan guard to use with spacers over the I/O board.

There is a version with a cutaway to allow use of the I/O board buttons and one without the cutaway.

Hugocraft designed the original 'cover' as a way to mount a fan without an I/O board and his bottom piece would be the matching piece to mine. [Link to original and bottom](https://www.thingiverse.com/thing:3184154)