Added a complete and an incomplete Perl 6 solution.

The complete solution works exactly as per the rules.
Conceptionally it's rather simple, the result is created
by appending to a dynamic variable, which is looked up
through the caller. This is functionally similar to a
global variable in this code.

I am calling the incomplete solution incomplete, because I
have not yet been able to make it work without the sigil,
which breaks the rules.