refactoring into multiple files, not tested on hardware

CMakeLists.txt

@@ -40,6 +40,9 @@ if (TARGET tinyusb_host)
                 hello_usb.cpp
                 display.cpp
                 commands/echo.cpp
+                keyboard_input.cpp
+                command_processor.cpp
+                epaper_manager.cpp
                 )
 
     add_subdirectory(pico-ssd1306 commands)