An opinionated list implementation, in the questionable code style of École 42.

	      t_doubly_linked_list             t_element_container

	+-------------------------+          +-------------+-------+
	|                         |          |               next +-----> NULL
	|                    head +--------->+   content           |
	|  size                   |          |               prev  |
	|                         |          +---------------^-----+
	|                    tail +----+                     |  |
	|                         |    |     +---------------+--v--+
	+-------------------------+    |     |               next  |
	                               |     |   content           |
	                               |     |               prev  |
	                               |     +---------------^-----+
	                               |                     |  |
	                               |     +---------------+--v--+
	                               |     |               next  |
	                               +---->+   content           |
	                                     |               prev +-----> NULL
	                                     +---------------------+