closes#6604
* Default for `to` was always `(from-1) + limit`. This caused a problem
where the `to` value could be higher than the length of the number of
blog posts, causing `@last` to never be called/reached
* Now sets `to` to have a default of `length` and if a limit was sent
through and not higher than `length`, to then set `to` to that value
* Added some extra tests for `@last` and `@first` use cases
* Added some inline commenting