Mass edit: artist "c"

I'd like to mass edit c (95 posts) to c_(neta) (from Twitter/email), because a single char is a bit... short.

FYI, he pronounces his own name as "シィ(Shii)." (From his PiXA profile. )

That'd be consistent with how "c" is pronounced (approximated) in Japanese, so it's an entirely reasonable spelling.