add singly linked list

Signed-off-by: Mattias Andrée <maandree@operamail.com>
add tailless singly linked list

Signed-off-by: Mattias Andrée <maandree@operamail.com>
m

Signed-off-by: Mattias Andrée <maandree@operamail.com>
reduce duplicate code

Signed-off-by: Mattias Andrée <maandree@operamail.com>
add doubly linked list

Signed-off-by: Mattias Andrée <maandree@operamail.com>
add tailless doubly linked list

Signed-off-by: Mattias Andrée <maandree@operamail.com>
m doc

Signed-off-by: Mattias Andrée <maandree@operamail.com>
preparation for circularly linked lists

Signed-off-by: Mattias Andrée <maandree@operamail.com>
add circularly linked lists

Signed-off-by: Mattias Andrée <maandree@operamail.com>
add headless linked lists

Signed-off-by: Mattias Andrée <maandree@operamail.com>