Make it possible to test custom scripts

[AlexDaniel]

See https://gfldex.wordpress.com/2019/03/25/i-like-rakudo-100x/

Basically, running blin.p6 WWW already does half of the job, we just need to add a way to provide a custom script that will be tested as a fake module. In this case it is:

use WWW;
my @stations;
@stations = | jpost "https://www.perl6.org", :limit(42);