Functions that end up calling a `malloc' or `realloc' return the new
struct `Result' which indicates if the memory allocation or reallocation
worked or not. If not, it holds a message, otherwise it holds the value
the function is meant to return (can be a null pointer if the function
returned a `void' before). The library will no longer forcibly exit the
program on such error in case it can be recovered by the code calling
it.
The modifications described above lead to vector-creating functions
returning a pointer to the newly created vector, and the function for
deleting vectors also frees the vector.
This commit also inlines some functions to make the compiled code a bit
lighter and calls to these functions possibly a bit faster.
`PDEB' is redefined following the new `PCOMMON' macro that is also used
by `PERR' for desplaying debug error messages.
Some lines are also modified to avoid potential memory leaks in case of
a memory (re)allocation.
