feat: hoodie.plugin

Adding a method to add 'plugins' to hoodie object. Plugins can be passed as a
function (a callback that will recieve hoodie as a parameter) or an object (the
key will be the method name, and the value is the function). Plugin calls can be
chained to add multiple plugins. See README.md for examples.

closes #2

index.js

@@ -29,6 +29,7 @@ function Hoodie (options) {
   api.task = new Task('/hoodie/task/api')
   api.connectionStatus = new ConnectionStatus(api.url)
   api.log = new Log('hoodie')
+  api.plugin = require('./lib/plugin')
 
   api.on = require('./lib/events').on.bind(this, state)
   api.one = require('./lib/events').one.bind(this, state)

lib/plugin.js

@@ -0,0 +1,15 @@
+module.exports = function pluginMethod (plugin) {
+  var self = this
+
+  if (typeof plugin === 'function') {
+    plugin(self)
+  }
+
+  if (typeof plugin === 'object') {
+    Object.keys(plugin).forEach(function (key) {
+      self[key] = plugin[key]
+    })
+  }
+
+  return self
+}