Added Category and Best Sellers Search
Updated API interface and added category and best sellers search. Useful for obtaining ASINs from Amazon.
For keepa details, see:
https://keepa.com/#!discuss/t/request-best-sellers/1298
https://keepa.com/#!discuss/t/category-searches/114
Example
import keepaAPI
api = keepaAPI.API('key') # input actual key from https://keepa.com/#!api
categories = api.SearchForCategories(r'Home')
bestsellers = api.BestSellersQuery('9568356011') # catID from categories in previous line