Surprisingly smooth first attempt at this

COC-1 #time 40m

I can draw an arc that starts as a point, completes a full circle, and
then resets to a point. Currently it's not:
1. In the right spot at all
2. Affiliated with units in any way
3. Using attack speed to determine loop speed

And other things that would be tedious to list.
Add cooldown percentage method to attacking unit

For the moment, this is only useful to help me determine how much of the
timing arc to draw around a unit. It might prove useful in other
circumstances later.
Draw cooldown timer loop on every unit

The length is based on the time elapsed since the units last attack. At
the moment, everyone has the same attack speed, and range isn't factored
into an attack, so everyone's loop are exactly in sync with eachother.
Slow Archer's AS to show different cooldown loops
Move units toward target based on range, not width
Consider unit range when trying to attack

Instead of only consulting cooldown, unit must also make sure target is
in range before attacking.
Fixed broken input processing

After I moved this to a separate file, it no longer had access to a
handful of the variables that it was referencing.
Remove some trivial comments.
Remove depreciated global fuse
Rename DefensiveUnit to Structure

This is more descriptive for the way I want to use it.
Make sure all created units have at least 1 hp

I almost "fixed" this in a very incorrect way but removing "is_alive"
check when drawing buildings.
Add Wall class
Ugly rough drawing technique for walls
Properly draw Wall based on being a Structure

Previously I was looking for an exact class match on Wall, because I
thought it was necessary for a reason I didn't understand. Fortunately
it was a problem elsewhere, and I can use the subclassing as I thought.
Add line of walls to defendingList
Set wall positions using array assignment
Fix Wall width error

I had only written "width" where I meant "self.width"
Fix ActiveUnit range issue
Remove noisy print statement
Make attackSpeed a private variable