clean player name before using it in filename.  prevents weird cases when
saving files with (possibly invalid) utf-8 sequences in them.  also strips
color codes because they render oddly on commandline.
also strip out ascii chars windows cannot handle in filenames.
use null instead of empty string
Merge pull request #509 from dpadgett/svdemo

[MP] svdemo: clean player name before using it in filename.  prevents weird cases whe...