Add methods to pull json data from SerpAPI wrapper

[Dr-Hutchinson]

Greetings! Thanks for all the work on a great library. A suggestion I'd recommend is the addition of separate methods to the serpapi wrapper to pull values from the SerpAPI json produced for searches. There's a lot of data in there that could be used to aid downstream tasks. Here's an example JSON. In particular, I'd be interested in methods to retrieve the 'snippet' and 'url' values, or to pull the search id values for each search to enable further API calls directly from SerpAPI's search archive.