refactoring output
adjusted CMakeLists.txt so that the library installs to /usr/local/lib and the headers to /usr/local/include
fixed ALIGN() macro
removed unnecessary assignments in list_take()
refactoring
fixed container_of() - macro so that it now is possible to directly access a member field of the returned struct
+  Fixed a bug in the avltree impl. which messed up the parent pointer of the nodes on rotation. + Added macro avltree_for_each_postorder() to iterata over all elements stored in the tree. Also added an corresponding test case for this macro