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
> strings can be found in std.algorithm and std.range.

It should also mention `array` (eg: `front`, `popFront`). Also (IMO), they should be mentioned in increasing order of genericity, eg:

> can be found in std.array, std.range and std.algorithm.

Of course, nitpicks. Thanks for doing this.