Allow for duplicate keys in QueryParams

[Knugel]

Fixes #365.
This PR changes the way QueryParams are parsed from JSON.
As JSON requires unique keys only the last value is returned in case of duplicates.
By using a JsonTextReader instead of JsonConvert#DeserializeObject this behaviour can be changed.

[thinkingserious]

This is awesome @ImbaKnugel!

Do you mind adding a test or two :)

[Knugel]

I'm not sure how to properly test the methods without changing their visibility.

[mbernier]

@ImbaKnugel

We have not been able to merge your Pull Request, but because you are awesome - we wanted to make sure you could still get a SendGrid Hacktoberfest shirt.

Please go fill out our swag form before Nov 5th and we will send the shirt! (We know that you might have tried this before and it didn’t work, sorry about that!)

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[thinkingserious]

Hello @ImbaKnugel,

Thanks again for the PR!

We appreciate your contribution and look forward to continued collaboration. Thanks!

Team SendGrid DX