std.string doc issue11895

std.algorithm style doc header

https://issues.dlang.org/show_bug.cgi?id=11895

preview:
http://burner.github.io/phobos/phobos-prerelease/std_string.html
Oops, my mistake... the correct function name is `countchars`, not `countChars`. The current link doesn't work because of that.