Add template keyword to CROW_MIDDLEWARES macro

[The-EDev]

As mentioned in #365, Allows for app.route() to use template arguments. Though should make sure nothing is being messed up by that addition.

[The-EDev]

@dranikpg What do you think about this?

[dranikpg]

Oh crap, I totally forgot about this issue 😰 (#365 (comment)).

Giving the compiler a hint that the following function is a template function should theoretically not break anything. This is a good explanation where the template keyword should(can) be used.

The problem however is a bit more complex. Lets examine the following example:

template<typename App>
void run() {
    App app;
    CROW_ROUTE(app, "/secret")
      .CROW_MIDDLEWARES(app, SecretContentGuard)([]() {
          return "";
      });
    app.port(18080).run();
}

We need to make 3 changes to make this work:

#define CROW_ROUTE(app, url) app.template route<crow::black_magic::get_parameter_tag(url)>(url)
#define CROW_MIDDLEWARES(app, ...) template middlewares<typename std::remove_reference<decltype(app)>::type, __VA_ARGS__>()

I added two templates and one typename. Again, those changes should theoretically not break anything:

The syntax allows typename only before qualified names

std::remove_reference<decltype(app)>::type is a qualified name in any case, so typename is valid.

route() and middlewares() are template functions in any case, so template is valid.

Not sure yet about the websockets. I haven't used them much, so I don't have a lot of examples to quickly test on.