Clean code

[ghost]

With these 3 commits, I did a lot of things (it took me all day 😊 ) and I solved two issues:

• the Move js to a new file (Error: The character encoding was not declared. Proceeding using windows-1252.) #53 and
• the Move css to new file for cleaner and easier to read code #54

1. First I put the css code and the background image of the game in a folder that I called "css".
2. Then I created a "main.js" file where I grouped all the javascript code that was present in the "index.html". I placed it in a "src" folder with the "stats.js" file (already present in the project when I started working).
3. To make it work, I did import/export and I activated the "module" mode on the "script" tag that I created in the html file.
4. Finally I went through all the files to put all indentations in order.
   Everything worked when I tested it. 😃 Feel free to tell me if something is wrong.