Known CPU usage spikes

[NQNStudios]

I'm consolidating all excessive CPU usage problems into a single issue with a checklist. I'll be closing the other CPU-related issues, and if they reference specific measurable CPU spikes, I'll copy that content into this one.

• [ ] multiline text-input fields cause CPU to spike because they are calculating word wrapping every frame. Fixing this will involve repurposing the fix for word-wrapping here which for some reason wasn't directly applicable to field.cpp without a headache.
• [ ] Walking on lava spikes CPU
• [ ] The start of outdoor combat spikes CPU (because the map is being generated)

[CelticMinstrel]

I'm also going to note that replacing text-input fields with something from TGUI might be an option, maybe.

[NQNStudios]

Another thing we could do to help low-powered computers run it, is make the frame-rate reducible. This is easy in the code, we just need to add it to the preferences window.