The API documentation and search are still both in the user manual, the search is provided by google, however, which makes it prioritize end user stuff in the results automatically.
For example:
http://manual.calibre-ebook.com/news...ml#news-recipe
or
http://manual.calibre-ebook.com/plugins.html#plugins
But API documentation in calibre is only available for the parts that have well defined external APIs like the plugin system or the news download system. For the rest, you have to go spelunking in the code.