RFC: Param types
Currently one needs to parse manually param values AFAIK

```nim
get "/game/@id":
  echo (@"id").parseInt
```

We can somehow hint at least the cases when it's a number or a flag.

Something like this seems sufficient

```nim
get "/game/@id:int":
  echo (@"id")
```

or

```nim
get "/game/@id" do (id: int): # I am not a huge fan, because we need to write id twice
  echo id
```

