Adds varying levels of battle speed

[redice44]

I opted to add speeds up to 16x. When testing the speeds 4x still felt slow. 8x was better, but only at 16x did it feel fast.

My main concern at 16x is it's firing every 25ms, which can stress performance on some machines.

Issue: #97

[flesler]

You could switch the setInterval for a setTimeout and just alter the property that holds the delay/interval. Might be simpler