Add support for -on-build= and -on-fail=

This adds command line options for actions to be executed after successful builds and failed builds.

It lets you ring a terminal bell, or print an attention getting banner on a failed build.

It is also useful if you are working on a service for which you give a "restart" command rather than running it directly. -command does not appreciate commands which exit. For instance, at the moment I'm using

    CompileDaemon … -on-build="sudo systemctl restart mydaemonname"