Remove Null Fields from Response Objects

[davidvonthenen]

Proposed changes

Addresses #163

For all parameters we don't want to include when null, use a pointer for JSON parsing. Tested using the examples.

NOTE: Combining just in the interest of time. Also fixes an issue with Paragraph -> Paragraphs: https://github.com/deepgram/deepgram-go-sdk/pull/174/files#diff-6d6a17cac219ff3f71886cf5d9bc5b4803f75690ab397ba1f72863920080d191R96

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• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
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Checklist

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Further comments

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