Split up prep

[waveform80]

Having used prep for a bit, I've come to the conclusion I've committed the cardinal UNIX sin of doing too much in one tool. It needs splitting up:

• --size can be ditched; fallocate does that just fine anyway
• --copy and --remove can go into something like nobodd-cp and nobodd-rm. Perhaps add an ls and cat clone while at it
• cmdline manipulation should be made more generic; some sort of nobodd-cmdline tool that can "set" var=value (how to delete values?) in the cmdline.txt
• what about config generation? nobodd-cfg? Hmm... need to think about that one