Add 'init' and 'fullscreen' button

Hi, Jagthedrummer Nice to meet you.
I used the code mirror and looking for a project such as codemirror-ui.

I just added two simple functions, right now.
- init
Function to initialize the character in the editor and for the button.

- fullscreen
Function to display the editor to fit the window and for the button.

Please, have a look init and fullScreen method.