Randomize damage dealing/preventing, etc.

Changed the type of the NPC struct's "status_effects" array from int16_t
to uint8_t, incorporated randomization into the dealing and preventing
of damage, and made a few other adjustments, ultimately modifying the
following functions: "damage_player", "damage_npc", "cast_spell_on_npc",
"init_npc", "tick_handler", "adjust_player_current_health",
"adjust_player_current_energy", and
"graphics_select_single_repeating_click".