Update the Amazon API, fix missing parameter and response parsing.

This updates the AmazonSearchEngine module to comply with changes made to the Amazon API documented here: https://affiliate-program.amazon.com/gp/advertising/api/detail/api-changes.html

Changes were also made to better conform to PSR2 code styling and improve documentation.

I've tested this on a large library of just over 3,000 albums and it seems to work well as long as your ID3 tagging is accurate.

An Amazon developer public and private key is required as are an 'Amazon Affiliate Associate Tag', though these are free to request upon registration of a developer account (also free for the base level).