Drop support for Python 3.6 (#1004)

* Drop support for Python 3.6
* Remove unused time parsing function
* Use Python 3.7 datetime function for writing stats data conversion
* Test against Python 3.10 on macOS and Windows

novelwriter/__init__.py

@@ -209,9 +209,9 @@ def main(sysArgs=None):
     # Check Packages and Versions
     errorData = []
     errorCode = 0
-    if sys.hexversion < 0x030600f0:
+    if sys.hexversion < 0x030700f0:
         errorData.append(
-            "At least Python 3.6 is required, found %s" % CONFIG.verPyString
+            "At least Python 3.7 is required, found %s" % CONFIG.verPyString
         )
         errorCode |= 0x04
     if CONFIG.verQtValue < 50300: