This patch change the size of real array from 3 to 4 doubles. This patch
remove the length attribute. Now the size computed from the no-zero
value.

There is missing call to the finalize callback in observation system.
This patch fix the problem and provides new observation callback systems
based on function_ref. (Closes: #29).

Adding two global inline function pointers to allocate/deallocate
memory. This patch allows the use of external tools instead of default
malloc/free functions.