refactor to support multiple vms, closes #25

[nlf]

this needs a lot of testing, but i think it works

[nlf]

still todo

• [ ] make status print some short status for all vms if it isn't given a vm parameter

[ailispaw]

Can we share bzImage and rootfs.cpio.xz with multiple vms?

[nlf]

i thought about that, but i decided against it so that users can do things like create a new vm to test a new vm version. also i didn't want to make it so users have to shut down every vm to upgrade the os.

[ailispaw]

I see. Thanks.