The list that garbage-collect returns now has one additional
element. This is a cons cell containing two numbers. It gives
information about the number of used and free floating point numbers,
much as the first element gives such information about the number of
used and free cons cells.
The new function memory-limit returns an indication of the last
address allocated by Emacs. More precisely, it returns that address
divided by 1024. You can use this to get a general idea of how your
actions affect the memory usage.