Add functions returning starting/ending page

Add two functions, returing article starting page and article ending
page. Currently, pages are stored in single variable, which leads to
less then optimal medatada description, e.g. <meta
name="citation_firstpage" content="1-61"/>, with no citation_lastpage
tag.
Revert "Add functions returning starting/ending page"

This reverts commit d6f592a11199f288f9f2adcc903aab3cca18a0be.