Main window frameless + Switching to MSVC2019

Chronos.pro

@@ -7,10 +7,10 @@ CONFIG += c++17
 # remove possible other optimization flags
 QMAKE_CXXFLAGS_RELEASE -= -O
 QMAKE_CXXFLAGS_RELEASE -= -O1
-QMAKE_CXXFLAGS_RELEASE -= -O2
+QMAKE_CXXFLAGS_RELEASE *= -O2
 
-# add the desired -O3 if not present
-QMAKE_CXXFLAGS_RELEASE *= -O3
+# add the desired -O3 if not present, MinGW only
+# QMAKE_CXXFLAGS_RELEASE *= -O3
 
 RC_ICONS = icon.ico