Added avl.{c,h} files with first definition of the interface
Added implementation of avl_alloc(), which is just an alias for convenience
Fixup for initial import
Added infrastructure in avl_add() function
Fixup of the parameters of the find() and del() functions
Added helper function for finding elements
Added infrastructure implementation for avl_del() function
Added more comment to the helper function
Added implementation of the avl_find() function
Fixup for the initial import (argument types)
Added basic infrastructure implementation of the avl_unlink() function