Version 7
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There is a world with one randomly-placed, randomly-sized, stationary particle. 
There are buttons to play, step, and reset the model. Stepping the model causes 
the particle to move. Resetting the model places the particle at a new random 
location with a new random size. Playing the model causes it to step repeatedly.
Resetting the model causes it to stop playing. Once the play button has been 
clicked, it cannot be clicked again until the model is reset.
1. In the reset function, call the clearInterval
2. In the play function, add a line to disable the play button
3. In the reset function, add a line to enable the play button


Version 6
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There is a world with one randomly-placed, randomly-sized, stationary particle. 
There are buttons to play, step, and reset the model. Stepping the model causes 
the particle to move. Resetting the model places the particle at a new random 
location with a new random size. Playing the model causes it to step repeatedly.
1. Add an HTML button element for the Play button
2. Define a JavaScript function that is called whenever the button is clicked
	a. The function will call the step function repeatedly using setInterval


Version 5
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There is a world with one randomly-placed, randomly-sized, stationary particle. 
There are buttons to step and reset the model. Stepping the model causes the 
particle to move. Resetting the model places the particle at a new random 
location with a new random size.
1. Add an HTML button element for the Reset button
2. Define a JavaScript function that is called whenever the button is clicked
	a. The function will basically do what the onload function already does
	b. We also have to clear the canvas
3. Add and HTML element for the Step button
4. Define a JavaScript function that is called whenever the button is clicked
	a. Change the x and/or y position of the center of the particle by 1


Version 4
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There is a world with one randomly-placed, randomly-sized, stationary particle.
1. Get random numbers for center_x, center_y, and radius
2. Make sure the circle is inside the walls


Version 3
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There is a world with one stationary particle.
1. Make canvas bigger
2. Create a Javascript file
3. Link it to the HTML file
4. Add Javascript code to draw a circle on the canvas


Version 2
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There is an empty world.
1. Create an HTML canvas element
2. Style it using CSS (give it a border and background color)


Version 1
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There is no model yet.
1. Add our name
2. Add a description


Version 0
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1. Download the template
2. Upload the template to our public_html
3. Open the template in our web browser