v0.16.0

Changelog

• 7779d4e: Attribution headers in cmd/blick; README defers the Go version to go.mod (@anderix)
• da1f5fc: README: presence paragraph without the attention preface (@anderix)
• 8113aa8: blick tray --autostart yes|no writes or removes the login entry, and the tray refuses arguments it does not know; README gives Debian's AppIndicator setup (@anderix)