Type-enforced sorted lists and related functions.

These are useful for:
* Constraining the argument of a function to be a sorted list by stating in
  your type that the input list is a sorted list.
* Avoiding sorting a list twice.
* Creating a list that is sorted from the moment of its construction, so it
  doesn't have to be sorted later.
* Performing list operations keeping the input list sorted.
* Improving those list operations that can be benefited from the ordering
  of its elements.
* Creating infinite lists that are sorted!
* And more!