added simple object model for lights

Just playing around, so this probably isn't as well thought through as it could be, but it's definitely a step forward in easy of control.   I've added a Light class to the Client which provides an object oriented interface to a single light.  You can now do things like the following in the console

    [7] pry(main)> client.lights
    => {"1"=>{"name"=>"Hue Lamp 1"},
     "2"=>{"name"=>"Hue Lamp 2"},
     "3"=>{"name"=>"Hue Lamp 3"}}
    [8] pry(main)> my_desk = client.light(1)
    [9] pry(main)> my_desk.name
    => "Hue Lamp 1"
    [10] pry(main)> my_desk.name = "Ken's Desk"
    => "Ken's Desk"
    [11] pry(main)> my_desk.bri = 255
    => 255 # and light gets bright
    [12] pry(main)> my_desk.bri = 10
    => 10 # and light gets dim
    [14] pry(main)> my_desk.hsl = Color::RGB::Orchid.to_hsl
    => HSL [302.26 deg, 58.89%, 64.71%] # and light turns a nice pink color