Add dbus "gamma" driver

[micolous]

This pull request implements a new gamma driver for Redshift which supports DBus signal output.

This allows you to use Redshift's day/night calculations in other applications, for example, networked lighting control systems.

This is not a full DBus control implementation like #54, but rather something extremely basic to emit signals. For example, the object does not even implement introspection. It only emits signals and doesn't allow control of any kind.

The signals look like this when emitted on DBus:

$ dbus-monitor --system "type='signal',sender='dk.jonls.redshift.dbus',interface='dk.jonls.Redshift'"
signal sender=org.freedesktop.DBus -> dest=:1.3994 serial=2 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameAcquired
   string ":1.3994"
signal sender=:1.3742 -> dest=(null destination) serial=5994 path=/dk/jonls/Redshift; interface=dk.jonls.Redshift; member=Temperature
   int16 3500
signal sender=:1.3742 -> dest=(null destination) serial=5995 path=/dk/jonls/Redshift; interface=dk.jonls.Redshift; member=Temperature
   int16 3500

This can be used with a program which connects to DBus, listens for the signal, and then the message can be used appropriately. This can also be used on embedded systems without Xorg.

Documentation for use is included with this pull request.

[jonls]

Thanks. Does this provide the same signals as the hooks? Or does it provide additional information?

[jonls]

Closing due to inactivity.