implemented the singleton pattern
added access modifiers
removing whitespace between exit and the parens
updating a code comment
removing whitespace at the bottom of the file
combining both the admin_open and admin_close into a single file. localizing the text.
removing the open/close files and combining them into a single admin view
initializing instance to null, initializing the plugin_screen_slug to null,  updating coding conventions, improving comments, updating conditionals,
disable the admin menu by default