feat(cmd): add start command

adds an initial start command. It works so time to add docs.

    ./corectl start hello '/bin/sh -c while true; do echo hello world; done'
chore(cmd): go fmt list_units
chore(cmd): cleanup the import
feat(cmd): add a logger
feat(cmd): add command descriptions.
feat(cmd): have start load full unit files from disk

this doesn't actually work against the current version of coreinit
but will once coreinit can take in a full unit file.
refactor(target): Assume user provides full service file in job
feat(corectl): Add corectl stop command
chore(README.md): Update README.md to reflect reality
Merge pull request #14 from bcwaldon/full-service-files

Add corectl start cmd; pass full service files in job payload