Request.params do not allow duplicate parameters
https://github.com/dom96/jester/blob/d8a03aa4c681bc8514bb7bbf4953d380d86f5bd6/jester/request.nim#L95

Sometimes, in query strings, you need to pass lists. This is generally done by duplicating the same key over like: `name=a&name=b`. juster folds these into a single parameter in the above code. Instead of using `[]=` to add new parameters, `add` allows key duplicates.