Feature request: Support repeated query parameters

[alexfoxgill]

Repeated query parameters are useful for representing lists. For example, /filters?filter=a&filter=b

https://runkit.com/5b2bbe0e6bb7720012426f93/5b2bbe156bb7720012426f98

[Floby]

This might be interesting, but I don't really have the time to spend time on it :s I'm happy to review a pull request nonetheless.
It might be interesting to make it explicit and have the method called appendQuery or something.

[VariableVasasMT]

#13