Various small fixes/enhancements/changes

Currently:
* Bugfixes
  * Fixed [issue with canonical links](http://wordpress.org/support/topic/serious-canonical-issue-with-paginated-posts) on last page of paginated posts - props [maxbugfiy](http://wordpress.org/support/profile/maxbuxfiy)

* Enhancements
  * Added 'wpseo_breadcrumb_single_link_with_sep' filter which allows users to filter a complete breadcrumb element including the separator - props [Jrf](http://profiles.wordpress.org/jrf). 


But I kind of expect this pull request to gain some more before you're back from your holidays ;-)