Add new handler types to better support spring and spring boot

[xfeep]

Related to #274 . This feature has these goals.

1. Support spring framework powered nginx clojure/java/groovy handlers
2. Add nginx spring auto starter project to be more friendly to spring boot web projects.
3. Better unit testing experience when using spring boot and nginx-clojure-embed

e.g.

  location /myapi {
     rewrite_handler_type spring;
     ## MySpringPoweredRewriteHandler is an rewrite handler powered by spring framework, e.g. by dependency injection
     rewrite_handler_name example.MySpringPoweredRewriteHandler;
  }

  location /spring-boot-web-app {
      content_handler_type spring-boot-web-app;
      ## example.MySpringBootApplication is a standard spring boot web application.
      content_handler_name example.MySpringBootApplication;
  }