Add sponsored search results and Pandas DataFrame conversion

[engjellavdiu]

Summary

This PR adds two new features to the library, as suggested in Issue #11:

1. Sponsored search results: The search function now accepts a sponsored boolean flag to fetch sponsored search results.
2. Pandas DataFrame Conversion: Introduced a to_df function to convert search results into a Pandas DataFrame.

Changes

• Modified SearchResult class to include an is_sponsored attribute.
• Updated the search function to accommodate the sponsored flag.
• Added a to_df function to convert search results to a Pandas DataFrame.
• Updated README to reflect these changes.

How to Test

1. Perform a search with the sponsored=True flag.
2. Convert the search results to a Pandas DataFrame using the to_df function.

Issue Link

Closes #11