--author option and amazon book rank

The --author option has been added (bkz.rb and amazon.rb) to allow for more accurate searches (only use last names) in amazon.rb. I have not added any improvements for google-books.rb or goodreads.rb, but those should be updated as well for increased accuracy.

Amazon book rank has been enabled for <1M and >1 thousand rank, but needs to be improved to enable all 42 million books ranks to be added. There seems to be a syntax error in obtaining the numbers and I don't currently know how to fix it with my limited Ruby knowledge.

* A new column must be added to the database for amazon book rank to work.