Generic intrusive linked list class.

Generic intrusive linked list class.

This commit is the initial implementation of the intrusive linked list
class.  It includes the implementation in the header files, and unit
test.

The iterators are circular: incrementing end() gives begin() and
decrementing begin() gives end().  Also made it valid to
decrement end().

Expliticly defines move constructor and move assignment
- Visual Studio 2013 does not implicitly generate the move constructor or
  move assignments.  So they need to be explicit, otherwise it will try to
  use the copy constructor, which we explicitly deleted.
- Can't use "= default" either.
  Seems like VS2013 does not support explicitly using the default move
  constructors and move assignments, so I wrote them out.