added 'dump' command

creates a file in /tmp/memc-dump_$(uname -n)_<ms>_<uuid>
with two columns: key size-bytes
added ycm conf file
updated dump command
max item size 1<<27
changes to slab allocation

enforce mem limit more strictly; if first item to class arrives
don't allocate first slab for class if we risk violating mem limit

also added many comments to explain what is going on