Rework to-hit chances

**What do you want to see?**
Right now the game just adds up a bunch of accuracy and evasion modifiers and takes the result to be a percentage chance to hit. That's not very balanced. I'm thinking instead we should do this:

1. Add up everything that makes it easier to hit (positive accuracy modifiers, negative evasion modifiers). Call that A.
2. Add up everything that makes it harder to hit (negative accuracy modifiers, positive evasion modifiers). Call that D.
3. Compute the formula: A / (A + D). That is your chance to hit.
4. If A and D are both zero, the chance to hit can be 50%, since if they were both, say, 42, then it would be 50%.

**How would it help players?**
To-hit modifiers would not be insanely OP, and we could use arbitrary numbers without breaking the game.

**Alternatives**
???

**Screenshots and mockups**
N/A

**Things to consider**
Should we keep the minimum 1% and maximum 99% hit chances?