Tank March

With the new AI code actively attacking cities, I noticed that it captures its city right after you capture yours. Thus both "marching" sounds also play concurrently. To my ear this sounded bad!

To fix this , I have started converting to a global sound manager. I say "started" because I only converted the "marching" sounds. I could do everything, but this was the only part causing a problem. Maybe in the future. For now I have more game mechanics I want to add!

A note about memory: I keep seeing this crash on Safari with "using too much memory".  I haven't seen this on other browsers yet, though I primarily use Safari so it could just be sampling bias. If you are reading this and play the game, and you see a memory error, please comment and let me know your browser + version.