refactor: add c++17 standard to project and c++14 to sylvan

CMakeLists.txt

 # set minimum cmake version
-cmake_minimum_required(VERSION 3.5 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.8 FATAL_ERROR)
 
 # project name and language
 project(pmc-sog C CXX)
 
-# compiler flags
+# C++17 standard
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_CXX_EXTENSIONS OFF)
+
+# Add compiler flags
 if(CMAKE_COMPILER_IS_GNUCC)
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fpermissive -std=c++17")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fpermissive")
 endif()
 
 # add pn parser

src/CMakeLists.txt

 # set minimum cmake version
-cmake_minimum_required(VERSION 3.5 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.8 FATAL_ERROR)
 
 # include MPI
 find_package(MPI REQUIRED)

sylvan @ 97208c7f

-Subproject commit 7184c4aede8b1d95c33442862075b37f9eaae899
+Subproject commit 97208c7f528f08a91afa99da0d43c6734d36cfa4