Added files for linkedlist implementation
We insert at the head of the linkedlist
When inserting at the head, we shouldnt call this append
Added implementation for ll_insert()
Added implementation for ll_insert_data()
Added implementation for ll_element_alloc()
Added implementation for ll_element_alloc_new()
Added implementation for ll_element_destroy()
Added implementation for ll_delete()
Added implementation for ll_destroy()
Added implementation for ll_foreach() (macro)
Fix: If the first element gets deleted, we have to re-set the head pointer
Fixup: Remove allocator
Updated implementation: Don't check the HEAD in the iteration
Merge pull request #35 from matthiasbeyer/add-ll

Add linkedlist