[Cmake] modernized cmake files a little bit

Author: FlorianReimold

fineftp-server/CMakeLists.txt

@@ -121,9 +121,10 @@ set_target_properties(${PROJECT_NAME} PROPERTIES
 
 ##################################
 
-# Mirror the folder structure in an IDE
-include(sourcetree.cmake)
-create_source_tree(${includes} ${sources})
+source_group(TREE "${CMAKE_CURRENT_SOURCE_DIR}" FILES 
+    ${includes}
+    ${sources}
+)
 
 ################################################################################
 ### Installation rules

fineftp-server/sourcetree.cmake

@@ -1,9 +1,7 @@
-cmake_minimum_required(VERSION 3.5.1...4.0)
+cmake_minimum_required(VERSION 3.13...4.0)
 
 project(fineftp_example)
 
-set(CMAKE_CXX_STANDARD 14)
-
 set(CMAKE_FIND_PACKAGE_PREFER_CONFIG  TRUE)
 find_package(fineftp REQUIRED)
 
@@ -18,3 +16,7 @@ add_executable (${PROJECT_NAME}
 target_link_libraries (${PROJECT_NAME}
     fineftp::server
 )
+
+target_compile_features(${PROJECT_NAME}
+    PUBLIC cxx_std_14
+)