More Client Modules and Request Methods

This pull request has:

* Methods to search for books using ISBN, LCCN, and OCLC numbers
* New modules for authors, revision history, and recent changes
* Two new request methods: query and history
* Tests and fixtures for all the new stuff

Still on my to-do list: More advanced queries, modules for editions, author works, and logging in, JSON callbacks, RDF support, and documentation.