switch on -O3 for Release build

CMakeLists.txt

@@ -38,6 +38,9 @@ if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
     "Debug" "Release" "MinSizeRel" "RelWithDebInfo")
 endif()
 
+#set(CMAKE_CXX_FLAGS "-Wall -Wextra")
+set(CMAKE_CXX_FLAGS_DEBUG "-O0 -g")
+set(CMAKE_CXX_FLAGS_RELEASE "-O3")
 
 # unit testing coverage, does not work yet
 #include (CodeCoverage)