[phobos] expand for std.metastrings

[Andrei Alexandrescu]

On 11/2/10 3:16 PM, kenji hara wrote:
> And, I do not recommend following use of expand:
> writeline(mixin(expand!"take $n times."));
>
> The probrem is:
> - expand concatenates string by ~ operators, it is may cost than using
> appender(text, formatWrite, writefln...)
>
> I will remove ddoc example from github code.

Expand should have an option to expand with commas and without 
to!string, i.e. in order to make the code:

writeln(mixin(anotherexpand!"take $n times."));

identical 100% with the code

writeln("take ", n, " times.");

Not sure what's the best name for "anotherexpand".

Andrei