Implement ToStr for char

[bstrie]

fn main() {
    println('a'.to_str());
}

This should print "a".

[Kimundi]

Currently, Ascii implements to_str() such that 'c'.to_ascii().to_str() == ~"'c'".
I guess that should better be changed to also return ~"c" to be consistent with this implementation, and because there is a repr module whose job it is to return ~"'c'" here.

[jjjjw]

This can be closed. <- I'm not sure if leaving such a comment is helpful?

[thestinger]

@oncemoreification: It's helpful, it ends up sending an email to people who are watching the repo.