use common header for fs

include/config.hpp

@@ -1,9 +1,7 @@
 #pragma once
-#include <experimental/filesystem>
+#include <fs.hpp>
 #include <json.hpp>
 
-namespace fs = std::experimental::filesystem;
-
 class config : public json {
   static fs::path &get_config_path();
   void create_config_directory();

include/data.hpp

@@ -1,9 +1,7 @@
 #pragma once
-#include <experimental/filesystem>
+#include <fs.hpp>
 #include <json.hpp>
 
-namespace fs = std::experimental::filesystem;
-
 class with_data_directory {
   void create_data_directory();
 

include/fs.hpp

@@ -0,0 +1,3 @@
+#pragma once
+#include <experimental/filesystem>
+namespace fs = std::experimental::filesystem;