added getAlephURL()
added getOCLCnum()
Added getISBN methods

* getISBNsAll() returns an array of all ISBNs
* getISBNjustOne() returns a single ISBN, favoring an ISBN-13 if found
* also added a new test book object and created an array $books to hold all the test books
* need to get unit testing going. Tests are getting out of hand
Added additional documentation to README

* added information about getISBNsAll() and getISBNjustOne()
* added information about getOCLCnum()
* some minor formatting