Rewrite the scripting support:

Add ruby classes that support scraper:
- ScraperKit::Scraper is the scraper defined in Ruby
- ScraperKit::Recipe allow define group of scrapers in Ruby, select by URL
- ScraperKit::RecipeRegistry allow choosing recipes based on input URL'

Add objective-C classes:
- IGScraper now only support using Objective-C to define scraper
- Add a protocol IGScraper, which have a scrapeWithHTML:url: method
- Add IGRecipeRegistry, that allow loading recipes from ruby classes, and select
and use scraper dynamically.
Update README, add examples.