Stop, pause, hibernate: kvbox

A box that is not in use can be put away three ways. They differ in what happens to its memory:

	files	memory	host RAM	comes back
`kvbox stop`	kept	gone	freed	`start`: a fresh boot, a few seconds
`kvbox pause`	kept	kept in RAM	still used	`resume`: instant, processes and connections intact
`kvbox hibernate`	kept	written to disk	freed	`wake`: well under a second, processes intact

pause is for a short break: nothing is lost and nothing has to be written, but the box still holds its RAM on the host.

hibernate is a snapshot the box takes of itself: its memory goes into a file next to its disk (only the pages it used, a few hundred MB for a fresh box) and the VM process ends. The box survives a server restart or a host reboot in that state, and wake brings it back exactly where it was, clock included.

stop is pulling the plug: processes are gone, files stay. stop on a hibernated box throws that saved memory away.

connect and exec resume or wake a sleeping box on their own, the way connect starts a stopped one. kvbox ls shows which state each box is in.