Once a battle has completed, update the existing tracker with the
gained evs.

EvSet object has no attribute “evs”. Update to use to_dict method to
return appropriate value for display.

Allows a specific EV value to be set directly on the active pokemon.

Command line called as such:

    ev set ev_stat ev_value
    ev set hp 14

Implement update method to allow a pokemon to be assigned an item or
“infected” with pokerus.

Allow set to be called from the command line with the intended options.