runctl: replace commander with getopt

Commander has non-standard handling of command line options,
posix-getopt implements the standard unix behaviour. Also, commander
formats long documentation strings badly.
runctl: load usage text from a file

Having it be in a text file instead of in javascript allows us to use
line-wrapping and other such text editing niceties (since js has no
notion of "here documents" or multi-line strings).