Assign path params before usage
Simple syntax:
```nim
pathParams:
  arg? int[m] = 100  # means that param "arg" is optional mutable integer with default value 100
  # We can use human readable syntax also
  arg1 string:
    optional
    mutable
    default = "Hello"
```

And in routes we just use:
```nim
"/user<arg>"
"/data<arg1>"
```