For some specific reasons I wanted not to escape the template
parameters. I was about to modify diet to provide an option of
not doing it, before I came up with quite an elegant trick.
Because Diet calls htmlEscape function to do escaping I realised
that I could pass my own symbol with the same name to override
the default behavior:
auto htmlEscape = (string a) { return a; };
res.render!("signup.dt", htmlEscape, data);