:disappointed_relieved:
Squash "warning: ambiguous first argument; put parentheses or even spaces"
Change 'previous' to 'prev'

"previous" is treated like "prev" by most user agents(maybe), but since
"prev" is officially listed in the specification:
http://www.w3.org/TR/html5/links.html#linkTypes, it should be used
instead of the long version.
PrevPage and NextPage don't use total pages and per page values
Use NextPage and PrevPage to generate link tags for rel=next and rel=prev

fixes #535, closes #509