Add support to other basic types than String in handler arguments

[Scorpiion]

Today this works:

  @Route("{?max}", method: GET)
  Future templates(String max)

But this does not work:

  @Route("{?max}", method: GET)
  Future templates(int max)

We should make this work so we support other types than String.

Current workaround:

  @Route("{?max}", method: GET)
  Future templates(int max) {
    var n = int.parse(max);