Implement mDNS discovery and use as default

[Siphonay]

On the Hue Bridge developer documentation, the mDNS method is listed first, and mentioned to have replaced the old UPnP approach.

https://developers.meethue.com/develop/application-design-guidance/hue-bridge-discovery/

I implemented it using Ruby’s stdlib mDNS resolver. Since it got added in version 2.1.0, I bumped the minimum version to that one.

I think this method is preferable as a default, because it does not need internet connectivity to discover Hue bridges on a local network, and is not subject to rate limiting or temporary or permanent outage of the online API.

The old method is still available as a fallback after a 10 seconds timeout, for example if the user’s router blocks multicast messages. The mDNS discovery can be completely bypassed by passing use_mdns: false to the Client initializer.

[soffes]

Thanks for doing this!

Tested it locally with this:

$:.unshift File.dirname(__FILE__) + '/lib'
require 'hue'

client = Hue::Client.new
light = client.lights.first
puts light

and was able to see a light. Also doing light.on! worked too. So I'm assuming it's good to go. Unfortunate there's not a better way to test this 😅 (Although that is totally outside the scope of this PR. Adding all this for future me.)

[soffes]

Available in version 0.3.0

[Siphonay]

Awesome, thanks for merging so quickly!