Use gorilla/mux for middleware and extend

- Use gorilla/mux for middleware.
- Add Dumper, RequestID, and Logger middlewares.
- Add makeURL helper

vendor/github.com/gorilla/mux/context.go

@@ -0,0 +1,18 @@
+package mux
+
+import (
+	"context"
+	"net/http"
+)
+
+func contextGet(r *http.Request, key interface{}) interface{} {
+	return r.Context().Value(key)
+}
+
+func contextSet(r *http.Request, key, val interface{}) *http.Request {
+	if val == nil {
+		return r
+	}
+
+	return r.WithContext(context.WithValue(r.Context(), key, val))
+}