Use smaller sample data files

[nwithan8]

Description

After banging my head against the wall about why in the world the HttpClient kept only getting the truncated XML data rather than the full set, and failing to trick GitHub's server to send me the entire payload, I finally realized the existing sample JSON and XML data is simply and unnecessarily too big.

This PR replaces the sample XML and JSON data files with smaller files, as well as introduces a sample HTML file. All unit tests in #77 have been rewritten to use these files rather than sample data from Reddit.

This PR needs to be merged first (blocks #77 )

Data courtesy of W3Schools, which Copilot slopped out in an auto-complete suggestion: https://www.w3schools.com/xml/note.xml

Testing

Pull Request Type

Please select the option(s) that are relevant to this PR.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Improvement (fixing a typo, updating readme, renaming a variable name, etc)