Add class of a page reference
Add find a page source method to DocumentSource
Issue #6: Support for link to prev and next page
format
Merge pull request #7 from kobo/issue/6

Issue #6: Support for link to prev and next page
cleanup
Issue #8: Support for referring to a local page
Improve PageReference constructor :golf:
Add license notation
Incoporate review comment
Merge pull request #9 from kobo/issue/8

Issue #8: Support for referring to a local page