ISBN

The ISBN class validates and converts the given string into a valid ISBN13 string.

Fix class has methods that can be used for the following functionalities,

1. convert the given string to ISBN10 string
2. Hypenate the given ISBN13 string
3. retrieving the check digits for ISBN10 and ISBN13 strings.

The ISBN class is rework of the following PYTHON library in JAVA

https://github.com/nekobcn/isbnid