Standard flexible linked list implementation

[iankronquist]

Currently there are separate linked list implementations scattered about the code base. Implement a standardized linked list which can be reused in different situations. Also implement the following functions:

void ll_insert(struct link *); // Does insertion sort
status_t checked ll_remove(struct link *);
struct link *ll_closest(struct link *, int (*compare)(void *a, void *b));
struct link *ll_find(void *, int (*compare)(void *a, void *b));
bool ll_contains(struct link *, void*);
void ll_push(struct link *, void *);
struct link *ll_pop(struct link *);

Also, replace at least one of the following:

• [ ] Linked list in devices (PR possibly pending)
• [ ] Linked list in processes.
• [ ] Linked list in vmem.c (alternately, replace this with an RB tree).
• [ ] Linked list in kmem.c (requires rewriting tests).

[iankronquist]

The names of those functions, their arguments, and return values are all flexible. Use your best judgement.

This should be a singly linked list.