Added perl environment (#311)

Perl runtime environment and example function.

examples/perl/hello.pm

@@ -0,0 +1,18 @@
+=pod
+
+You return a CODEREF from the package that will be called as your function.
+
+The code in the server is something like this (simplified):
+
+    my $sub = require('hello.pm');
+    $sub->(request);
+
+As you can see, you get the L<Dancer2::Core::Request> object as first argument
+to your function. You can use it to retrieve params given to your function or
+anything else Dancer2 offers. You can also use Dancer2 and use its DSL.
+
+=cut
+
+return sub {
+    return 'Hello, ' . (shift->param('name') // 'world');
+};