Adds Middleware API (#40)

* Adds test project

* Adds e2e for end-2-end tests

* Update gitignore

* Update loaders

* Creates test project

* v0.1.27

* Upgrade

* dependency fixes

* Load project plugins in the plugin loader

* Issue with instanceof

* Fixes versioning issues

* Adds medusa middleware api

* Adds documentation

* Fixes tests

e2e/prod-project/src/services/test.js

@@ -0,0 +1,16 @@
+import { BaseService } from "medusa-interfaces"
+
+class TestService extends BaseService {
+  constructor({ testModel }) {
+    super()
+
+    this.testModel_ = testModel
+  }
+
+  async sayHi() {
+    const res = await this.testModel_.create({ title: "hi" })
+    return res
+  }
+}
+
+export default TestService