• No more quotes or escapes for the start/finish messages, fixing #112.
• The start message was brought into Rust code rather than shell, so quoting doesn't affect it anymore! This may help a few other issues (e.g. #107).
• The finish message is printed regardless of whether the command is successful or not.
• On unixes only for now, the exit status is now reported as part of the finish message.
• LTO and codegen optimisations are now enabled for release builds.