Updating Abilities and AttackGenerators

This change mainly improves use cases for abilities and also makes the IAttackGenerator able to generate attacks for character based on all attack stats as per previous version, a new overload for passing in an ability to use, and one where you are given an existing damage type and need to augment that.

As part of this we have also brought in critical attacks to be a key part of the process as well as basic attack variance to add some randomness to the ouputs, although you can make your own versions if you want a more complex/simpler system.