New Plugin API

- Homebridge calls single exported initializer function and passes an
API object
  - No more require() for HAP classes (doesn't play well with plugin
structure)

.gitignore

@@ -6,3 +6,7 @@
 node_modules/
 npm-debug.log
 .node-version
+
+# Ignore any extra plugins in the example directory that aren't in Git already
+# (this is a sandbox for the user)
+example-plugins