Efficiency updates galore!

For the past 2 weeks or so, I've been evaluating the game to see what improvements I can make to it.

I've been looking into adding a proper ECS to it, replacing my old trusty sprite system, which is good but is now getting long in the tooth. I've also removed some of the sprites that the game has outgrown. This isn't a bad thing because it gives me room to do a few things:-

1. Improve the efficiency of the code. Removing unwanted entities means less duplication.

2. Provide space for adding a few entities I've been looking at adding for a while now - Tornadoes and Vikings.

Finally, I'm making a few changes to the HUD code - efficiency again!

Stay tuned for more!