proxy-audio-device: install audio driver

Fixes https://github.com/briankendall/proxy-audio-device/issues/13

This change does a few things to fix the installation of
proxy-audio-device, based on the README for installation:

https://github.com/briankendall/proxy-audio-device#manual-installation

- Install the audio driver to `/Libary/Audio/Plug-Ins/HAL`
- Kickstart `coreaudiod` on install and uninstall for the device to be
  available
- zap saved application state for the settings app

Casks/p/proxy-audio-device.rb

@@ -8,6 +8,33 @@ cask "proxy-audio-device" do
   homepage "https://github.com/briankendall/proxy-audio-device"
 
   app "Proxy Audio Device Settings.app"
+  artifact "ProxyAudioDevice.driver", target: "/Library/Audio/Plug-Ins/HAL/ProxyAudioDevice.driver"
 
-  # No zap stanza required
+  postflight do
+    set_ownership "/Library/Audio/Plug-Ins/HAL/ProxyAudioDevice.driver",
+                  user:  "root",
+                  group: "wheel"
+
+    system_command "/bin/launchctl",
+                   args:         [
+                     "kickstart",
+                     "-k",
+                     "system/com.apple.audio.coreaudiod",
+                   ],
+                   sudo:         true,
+                   must_succeed: true
+  end
+
+  uninstall_postflight do
+    system_command "/bin/launchctl",
+                   args:         [
+                     "kickstart",
+                     "-k",
+                     "system/com.apple.audio.coreaudiod",
+                   ],
+                   sudo:         true,
+                   must_succeed: true
+  end
+
+  zap trash: "~/Library/Saved Application State/net.briankendall.Proxy-Audio-Device-Settings.savedState"
 end