Exercise: In memory counter

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1. Create an application that has a button called 'Increment' and shows a number.
2. Every time the button is clicked the number increases by 1.
3. Implement it in a single HTML file without a 'script' tag.
5. Add another button called 'Decrement'.
6. When the user clicks that button the counter is decremented.
7. Still have this in a single HTML file without a 'script' tag.
9. Change the application now moving everything to a controller.
10. Both the initialization and the code of increment and decrement.
11. Disallow negative numbers: If the user clicks on 'decrement' while the counter
12. is at 0, display a message in a 'div' element that this operation is not allowed.