Add single-linked list (sllist)

We'd call it 'slist' but that's a reserved name in C++

Change-Id: I8527c01b03acd479fa115efeb2fa0f440bec04e5
Reviewed-on: http://review.couchbase.org/33943
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>