Create ToonAttackEvent class to create snapshot of a Toon's attack, target, and reward

[nosas]

The reward atk_hit and multiplier arguments will be passed in during ToonAttackState.handle_attacks()

This will allow us to easily calculate an attack's reward for each ToonAttackState.

[nosas]

We can utilize python's new dataclasses: https://docs.python.org/3/library/dataclasses.html

[nosas]

Done in #100