Add support for HTTP list parameters to request builder

[awswim]

Technically it's not a HTTP standard, but many APIs accept a 1:many relationship in HTTP parameters so long as those parameters have [] brackets.

Example supporting multiple user IDs:

api?user_ids[]=1&user_ids[]=34&user_ids[]=33

I'm adding support for those parameters to RequestBuilder.

[dylanrjames]

I've never seen this format before, seems a bit strange to me, but we can support it if it's not impacting anything else. Is there a more "official" name for this? Or can we use something more descriptive? ListParams seems a little strange to me, but maybe array params or something?

[awswim]

I called it MultipleValueParam, because the idea is that typically most parameters are 1:1 key:value pairs while these are 1:many key:value pairs.

Let me know if you think it would be better as ArrayParam or ManyValueParam.