add headamp class

examples/headamp/__main__.py

@@ -0,0 +1,18 @@
+import logging
+
+import xair_api
+
+logging.basicConfig(level=logging.DEBUG)
+
+
+def main():
+    with xair_api.connect("XR18", ip="mixer.local") as mixer:
+        mixer.headamp[8].phantom = True
+        for i in range(-12, -6):
+            mixer.headamp[8].gain = i
+            print(mixer.headamp[8].gain)
+            input("Press Enter to continue...")
+
+
+if __name__ == "__main__":
+    main()