Add a new --start-in-fullscreen command line flag

Fixes #856

kitty/boss.py

@@ -103,6 +103,8 @@ class Boss:
         if new_os_window_trigger is not None:
             self.keymap.pop(new_os_window_trigger, None)
         self.add_os_window(startup_session, os_window_id=os_window_id)
+        if args.start_in_fullscreen:
+            self.toggle_fullscreen()
 
     def add_os_window(self, startup_session, os_window_id=None, wclass=None, wname=None, opts_for_size=None, startup_id=None):
         if os_window_id is None:

kitty/cli.py

@@ -546,6 +546,11 @@ specify this address. This option will be ignored, unless you set
 option as it is read automatically from the environment.
 
 
+--start-in-fullscreen
+type=bool-set
+Make the initial kitty window fullscreen on startup
+
+
 # Debugging options
 
 --version -v