Middleware upgrade (#554)

* Adds root level middleware

* Added todo

* Better way for extensions to be added.

* Bad conflict merge?

fnext/setup.go

@@ -0,0 +1,40 @@
+package fnext
+
+import (
+	"net/http"
+
+	"github.com/fnproject/fn/api/models"
+)
+
+type Extension interface {
+	Name() string
+	Setup(s ExtServer) error
+}
+
+// NOTE: ExtServer limits what the extension should do and prevents dependency loop
+type ExtServer interface {
+	AddAppListener(listener AppListener)
+	AddCallListener(listener CallListener)
+
+	// AddAPIMiddleware add middleware
+	AddAPIMiddleware(m Middleware)
+	// AddAPIMiddlewareFunc add middlewarefunc
+	AddAPIMiddlewareFunc(m MiddlewareFunc)
+	// AddRootMiddleware add middleware add middleware for end user applications
+	AddRootMiddleware(m Middleware)
+	// AddRootMiddlewareFunc add middleware for end user applications
+	AddRootMiddlewareFunc(m MiddlewareFunc)
+
+	// AddEndpoint adds an endpoint to /v1/x
+	AddEndpoint(method, path string, handler ApiHandler)
+	// AddEndpoint adds an endpoint to /v1/x
+	AddEndpointFunc(method, path string, handler func(w http.ResponseWriter, r *http.Request))
+	// AddAppEndpoint adds an endpoints to /v1/apps/:app/x
+	AddAppEndpoint(method, path string, handler ApiAppHandler)
+	// AddAppEndpoint adds an endpoints to /v1/apps/:app/x
+	AddAppEndpointFunc(method, path string, handler func(w http.ResponseWriter, r *http.Request, app *models.App))
+	// AddRouteEndpoint adds an endpoints to /v1/apps/:app/routes/:route/x
+	AddRouteEndpoint(method, path string, handler ApiRouteHandler)
+	// AddRouteEndpoint adds an endpoints to /v1/apps/:app/routes/:route/x
+	AddRouteEndpointFunc(method, path string, handler func(w http.ResponseWriter, r *http.Request, app *models.App, route *models.Route))
+}