Add AppendQueryParam(s) methods

[Marusyk]

Fixes #688

Please review
Thank you in advance

[tmenier]

Wow, thank you for doing this. The main "problem" is you did it too soon. :) I just released what I'd consider the final 3.x versions and am embarking on 4.0 now. This one wasn't a high priority and my time is limited, but since you did it already I will try to get to it sooner than I otherwise would have.

One quick observation is I think about half the generated AppendQueryParam overloads should probably be AppendQueryParams (plural). It looks like you figured out how to auto-gen most of the code with that Metadata class, which is great.

So if you can be patient with me I will give it a more thorough review and merge it eventually. :)

[Marusyk]

Hi @tmenier
no problem put it on hold
in the meanwhile, I'll update AppendQueryParam -> AppendQueryParams

[tmenier]

A year on and this is finally merged...thanks again!