Recently Used List
------------------

http://cyber-dojo.org/setup/show_exercises/?language=C%2B%2B%20(clang%2B%2B)&test=GoogleTest

Develop a recently-used-list class to hold strings
uniquely in Last-In-First-Out order.

* A recently-used-list is initially empty.

* The most recently added item is first, the least
   recently added item is last.

* Items can be looked up by index, which counts from zero.

* Items in the list are unique, so duplicate insertions
   are moved rather than added.

Optional extras

* Null insertions (empty strings) are not allowed.

* A bounded capacity can be specified, so there is an upper
   limit to the number of items contained, with the least
   recently added items dropped on overflow.


