lua gives you a memory used number that only reflects the current allocations
if fact it doesn't even give you a way to get the amount of ram free
rb.mem_stats() seeks to fill this gap by marking the memory allocated for lua
with a sentinel value which can later be checked to get a high water mark
of the ram used by lua and a pretty good idea of how much ram is available
Also includes an example script
usage:
used, allocd, free = rb.mem_stats()
Change-Id: Ia282869f989848324d7d88c7df4827fdbce4fb4e
